Though I'm not actually sure WTF they classified BW over there as, since it's half sprites and half 3D models. It may be under their Models Resource site if you can't find it on the Sprite Resource side.
I'm not sure what you mean by "compatible". I draw my artwork in the FireRed style, which means that the dimensions are (usually) the same as what Emerald uses. The art style is something you'd have to decide for yourself, though, since Emerald and FireRed use different perspectives.