Currently with my Unholy DK, pet.Present() is only true when short-duration Shambling Horrors are up. In particular, it evaluates false when only my abom is up.

Also, is there a way to ask if your gargoyle/dark arbiter is currently up? There's no obvious buff that shows, so I would assume its in the same pet.* situation. Maybe an argument to pet.Present that identifies the class of pet?

I used to check for the CD of DA. And that way you can check if you cast it recently.
With CoF that was hell though. :)

There's no way to check for DA/Gargoyle in the API. The way it's typically done eg. in WeakAuras is you scrape the combat log for the spellcast event when you fire off the spell, and when you see it set a mod-local variable to true and start a countdown for the duration of the pet plus 5-6s for spawn animation and positioning. At the end of that countdown, set the variable back to false.