The pulley wobble in the rear (on a diff) is acceptable as the pulley is designed to wobble a small amount on the diff balls. The belt center's the pulley. Just like on a ball diff axle for pan cars. Without the pinion the spur gear wobbles. Once you put the pinion on it centers itself.

I would think that a gear wobbling on a layshaft is a problem and gear adaptor is a problem. There is no way for the gear to center itself. If the wibble is significant enough, you will fell a high spot. You can't tell this on an electric chassis cause the pinion gear does not free spin. (with a clutch system, fuel on-road, you can ratate the tires backwards and feel the gear mesh...God I Miss my MRX-4)

Place the gear on flat surface, glass and see if there are relatively flat. Keep in mind that nothings perfect.. If the gear is flat then it should be flat on the layshaft. If its not that the bolt pattern is warping the gear. Just ream out thole and problems solved.