So, here's a link to the dread ghast template, from the Advanced Bestiary.
Is this OK in PF terms (for monsters)?
To be honest it looks a bit overpowered for only a supposed CR1 boost. +4 Natural armor, Str +4, Dex +4, Int +2, Wis +4, Cha +6 plus a host of special goodies for only giving up your Con score.
I'd still considering using it but I'd figure it was closer to a CR+2 bump. Depends on what you add it to.
The Advanced Bestiary was a 3.5 product.
I believe that Paizo used those rules when they released the original Rise of the Runelords, for a particular bad guy in one of the modules.
When I converted that module to PFRPG, I created my own Dread Ghast template, that was a +2 CR template. I hadn't discovered the above online resource, but mine was pretty close to it.
Hal
I was thinking of adding it to the following:
** spoiler omitted **
Compare the last one with a normal ghoul, both are nominally CR1, but I'm pretty sure which one will do better in combat. The loss of Con doesn't affect the creature and it gets a whole lot of special abilities at a very low CR. I'd call it at least a CR2 and against low-level opponents could be deadly if the players are unlucky. Use with caution. (It could also be one-shot killed by a lucky first level character.)
The first one on the list will lose quite a few hp, but the ability boosts work well with it special abilities. So, its a little more balanced. CR4 base probably a strong CR5, weak CR6 creature. Against a suitable party, I'd be less worried that a couple of bad rolls would doom the party.
Remember CRs are just guidelines. You should always compare the result of any template with other creatures of that CR. It's easy to apply just the right template and create a monster that is overpowered for the mathematical CR result.
CR adjustments should never be used to min-max monsters, it defeats the whole purpose of estimating what kind of challenge you're throwing at the party.