Not allowing familiars to use UMD is a house rule, pure and simple. Familiars have intelligence scores without restriction on skills.
That being said- can a pseudo dragon use that particular skill- whether its a familiar or not?
From the UMD skill:
That is, you must speak, wave the item around, or otherwise attempt to get it to activate
Emphases on "wave the item around or otherwise attempt to activate it"
on Pseudo dragons themselves:
They speak draconic as a language so they do have the ability to speak.
The description says they /often/ only speak in chirps and such- not that they can't. and Draconic is listed in their languages.
Unless I'm missing something, I see no rule prohibition on them using the skill assuming they get ranks in it.
-S
Works for me... as a DM, if a player pitched it, I'd allow it.
Anything with an intelligence of 3+ can get skills. Some skills do have requirements on them (such as Fly requiring the ability to, duh, fly). However, that's about the only skill I can think of that has pre-requisites.
As pointed out, pseudodragons speak draconic, can learn any language, and can take any skill (including fly, by an odd coinkydink). They can use magical devices, and the UMD skill.
Now, magical items may require some work arounds. For example, when I let someone have a pseudodragon cohort, the cohort wore their rings as wristlets instead of rings. They wore anklets instead of boots. They wore a pouch of many pockets (size small) strapped around their waist, and a choker instead of a pendant (amulet of natural armor). Armor I didn't give them (although I suppose they could wear barding, so long as the weight didn't affect their flying).
The cohort had UMD and 3-4 wands (although she had cleric levels, so no need for UMD for her cleric wands). When she used a wand, she ducked her head into the pouch of many pockets and pulled the wand out with her mouth and waved it around and pointed it at the target and muttered the activation words around the wand.