as to point the first - sure. assuming the undead in question retains its intelligence, then there's not reason it couldn't work a forge, hammer metal, or scribe the occasional scroll of poetry. odds are that the transition from life to undeath is going to warp the perceptions and worldview of the now undead craftsman tho, so that might affect their creative process in strange ways. paintings would take on a darker tone, poetry would be perverse and twisted, jewlery would have a subtle taint/twist to it. so buyer beware.
point the second - again, sure thing...but you still have to stop and rest/recover spells. even the undead have their limitations. undead spell casters don't sleep...but they DO have to rest in order to regain spells. and spells is what fuels their magic item creation feats. additionally, it is likely that once again their undead state is going to color their creative process in odd ways. potions brewed by an undead horror would likely taste strange. wands would be carved from disturbing substances. scrolls penned in blood on sheets of vellum made from human skin. magic swords quenched in the blood of living victims. things of that nature. functional, but unpleasant to use.
1. Not only would this work, but it would make a damn fine adventuring hook.
2. Maybe longer in the creation process of the item, but from a magical reserve point of view, I don't think that it would be possible. In the same way that researching a spell could not be done with limitless mental reserve by an undead. Maybe for a longer time than a living humanoid with sleeping parameters, but not around the clock.
But then again, I haven't heard of any rulings on either subject.
No, undead casters can not spend more then 8 hours per day crafting a magic item. It doesn't matter how you justify it*, but there is a strict limit on how many hours you can work on a magic item per day. If undead weren't subject to that limit, there would be something saying so. Since there isn't, that limit applies to all casters, living or undead.
The caster can work for up to 8 hours each day. He cannot rush the process by working longer each day, but the days need not be consecutive, and the caster can use the rest of his time as he sees fit.
*Maybe because its tiring. Or maybe the process of enchanting an item is delicate, so the item can only handle so much progress per day, and trying to pour too much magic into it at once destroys the object. Or maybe its just some sort of balancing mechanism that has no in-game explanation.
It's for balancing.
Ring of Sustenance, undead, elven trance, and caffeine have been around long enough that if one of them allowed you to bypass one of the general rules of item creation, it would be called out in the specific item/creature/ability text.
Personally, I would assume that any undead with either a feeding habit or a death grudge simply would not have the patience for such a thing, and mindless and incorporeal undead just don't really have the ability to at all.
A ghoul is constantly hungry, unless it had a stock of fresh food on hand, it would be out the door hunting. And if it did have such a stock, it wouldn't be working, it would be eating. They can get stuff done in the calm points between, but I can't see a ghoul locking itself in a study for a week to churn out product. It would take an exceptional will, and by exceptional, I mean more than +10 to will saves. It would be an anomaly, not a commonality.
Same with those with a death grudge. A ghost is either haunting the bejebus out of its murderer, or its moaning in a corner missing its living existance.
Basically, of the more "common" undead, I can only see Liches being in any way capable of exceeding human productivity in the mundane and magical craft industries.
A mummy might, but that begs the question of why, since they are most often guardians. Although a mummy who forges weapons to wield in it's duty could be interesting. An oddly driven bodak might, and some devourers are obsessed enough despite their soul hunger, but most ghouls and vampires are too busy looking for the next meal.
Still, this thread has given me the idea of a mummy forgemaster who guards a long forgetten crypt in Osirion. He can be commissioned to make weapons, if you ask with due respect. Attempt to delve further into his crypt at your own peril.
Any lack of agreement on point two is only because people aren't paying attention. You cannot, cannot, cannot, craft magical items for more than 8 hours per day. Not as a vampire, not as an elf, not as a lich, not as a god. The rule is not there for logical fun, it's there to balance magic item creation, which is already hideously powerful.
And, actually, only one person of six disagreed. That's a pretty strong consensus. ;-)
Also, I figure I'll add a bit of light to your first question. Anyone can work around the clock to craft something using the craft or profession skill. They do not, however, gain any additional benefit for doing so past what is already defined in the craft and profession skills. Both of those skills specify that a solid, dedicated week of work must be taken to work on the item or items in question. There is no reason to think that the crafter undertaking this process is not already working as much as they can. While it is assumed that this is an 8-hour work day, there is no evidence in the text supporting this assumption that I am aware of. More likely, it's our modern-day eight hour work day transitioning in because that's what we expect. Fantasy work days aren't necessarily 8 hours. That's up to the GM decide.