Can I use nut meal or nut butter as a curry base?
I think it may work in some sense, but the results will be pretty different. Nut butters don't have a lot of starch in them. They thicken a liquid just by dispersing their solids. So 1 tablespoon of nut butter isn't going to have near the same thickening power as 1 tablespoon of flour. If you add enough to thicken it substantially, it will taste strongly of whatever nut you use (which may be good).

If your friend is specifically trying to avoid gluten, there are many other things you could use to thicken your curry. Rice flour would be an excellent choice, or cornstarch, or xanthan gum.