Spell trigger items and monsters with spellcasting.

[Yqatuba]

Can monsters with innate spellcasting (i.e not just SLAs but like how most true dragons can cast spells as a sorcerer of a certain level) use spell trigger items for whatever class they cast as without needing a Use Magic Device check?

[Diego Rossi]

It depends on the monster.

CRB wrote:

Spell Trigger: Spell trigger activation is similar to spell completion, but it’s even simpler. No gestures or spell finishing is needed, just a special knowledge of spellcasting that an appropriate character would know, and a single word that must be spoken.

Monsters capable to speak, like dragons, can surely trigger them (it must be actual speaking, not parroting, that was cleared for familiars).

With GM permission, monsters that can make sounds could have specially made Spell trigger items that react to a roar, a bark, or some other sound they can emit.

[Ryze Kuja]

Generally speaking, no. Spell-casting Monsters typically only know 1 to 10 spells or SLA's tops. Creatures like these would need levels of that class or access to the class's spell list somehow.

Dragons yes, they're sorcerers. Also, if you look at a monster entry and see a litany of more than 10 spells that they can cast (or have prepared), then absolutely, treat them as if they are that class for UMD purposes.

^---- none of that is RAW, just my opinion.

[Azothath]

The rules are generally focused on the PCs. Some monsters can, like humans, most can't.
Paizo Organized Play went through a few iterations to come up with a list of what Familiars & Animal Companions could use late in the game lifecycle. The Animal Companions Magic Item FAQ. I'm not going to totally agree with their criteria (as having humanoid hands is too restrictive) but the list is a good place to start.

Generally you'd like to see some spellcasting ability (not SLAs) or a spellcasting class.
There's nothing to prevent a monster race from having a hag or magic crafter make an item that responds to their native tongue or desire(use activated). It just has to be reasonably possible in your game.