That being said, your post makes it sound like Ritual (Animate Trees) is a better idea than I thought it was. So, yay.
That does leave it open for the Treant to do a lot more cool things in DFRPG than it could do in D&D, but that may not be what every GM will opt to do.
We need to make a custom power that grants you access to one spell and one spell only (or at least a limited list) if we want to convert D&D characters to DFRPG ones. I'll give it a try soon. Suggestions are welcome.
I had to (for sanity's sake) ignore some of the spell-like abilities when I was converting the Nyambe demons, except when I could find a clear Power. Some of them had spells like
poison, so I just added the Venomous quality onto their Claws power.
But generally, D&D creatures have either a small handful of key spell-like abilities, or a great big pile of them.
Some of those spell-like abilities are really more appropriate to a tactical game like D&D.
Others just don't translate well into DFRPG, like any of the
teleport spells.
Still others aren't in line with how DFRPG/DV treats those types of supernatural creatures (Demons/Devils/Fey/etc.).
Also consider that those abilities in D&D don't act like they would cost stress.
At the same time, some of those baddies only ever get a chance to pop off with 3-5 of their precious spell-like abilities before they get taken down.
At the end of the day, I think it's probably best to give Sponsored Magic to the monsters with big piles of spell-like abilities. For those with a few signature abilities, try to find or create powers to take the place. For anything in between, find a middle ground between Sponsored Magic, Evocation and Thaumaturgy.