This whole area should NEVER be assumed is ok. It would be like having someone stick their finger in your eye, then asking later if that is ok, and/or ignoring the fact that you tell them it is not ok and just keep on doing it. As far as part of GFE at all, I would say no. It might be something a greek provider is open to. I would put it as part of a PSE tho, for those who offer it. Like anything, this is something you should be asking about before you start poking your fingers or tongue into anything at all lol.
Also, be extremely careful of trying to combine DATO with DATY. Transferring bacteria from anal to pussy can be extremely harmful, in terms of infections. I would say the same thing about combining DATO with kissing. Just be aware of what you are doing and try to take some precautions; also to be aware of the "ick" factor. I am not too sure of how many people, m or f,, who would welcome the idea of kissing someone who has been licking their ass. A little courtesy and common sense goes a long way.
There are far too many unpleasant byproducts of DATO, like exposure to parasites and hepatitis, that make it a really bad idea. But along with that is the fact that many people simply do not want anyone poking around down there, find the sensation unpleasant, and if you are expecting someone to enjoy what you are doing, you should know that going in to always ask first before you do anything whatsoever.
And I suggest that if you are a fan of giving and receiving DATO, the very first thing you should get are the hepatitis shots. This will ensure, at least for some part, your continued good health.
Oh, and in case anyone was confused by my post, if anyone ever tries to do this with me (consider, I tell you up front it is a no go zone) I will hurt you lol. Be prepared for a very strong and negative reaction from anyone you try this on without asking first.