The important thing about choosing trucks for your e-board is the compatibility of the truck clamp you choose. The standard truck and truck clamp combination is a flat bottom design – this is to give the clamp somewhere to hold. If you had round trucks it would be much more likely that the clamp would slip.
Other than the clamp compatibility, just treat the trucks like you would in a normal longboard (e.g. width and bushings).
Furthermore, if you are a pro DIY’er then you could always weld a homemade motor mount to the trucks. This way compatibility is less of an issue and you could fit this to any kind of truck.