I'd look at an self leveling elastomeric sealant rather than grout. Sika is a good brand of elastomeric and is sold in caulk tubes. It comes in tan, grey and red. You need to put a foam rubber "backer rod" in the joint before you seal it so it doesn't take fourtyleven tubes of sealant. The elastomeric will move with the shifting and settling. I don't know of any reason this shouldn't be done around a pool, but if someone can give you a good reason, listen and decide for your self.

Good luck!

Pappy