Of course you can use NiMH batteries on brushless motors. Electricity is electricity; it doesn't have "flavors" that a particular motor won't like (e.g. EEEEW! Grape! I hate grape!
). Also, if you have only seen LiPolys recommended for brushless motors, you haven't been looking very hard... NiMH is still a very popular choice for budget minded and cautious fliers.
Just like with the LiPoly batteries, the NiMH you choose will depend on how much current you're expecting to draw.