Yes, you can certainly use two (or more) motors (of any kind) on the same shaft. Sharing one controller (with the two synchronous motors on the same shaft) might be possible if the motors are connected to the shaft matched in phase (depending on whether or not imperfect current splitting in the parallel motor connection causes problems) but there is rarely a reason to do this because it's rare to have such a large controller/inverter.
I suggest asking Cascadia about this, both because they made the controller, and because their motor division has lots of experience with two Remy/BorgWarner HVH motor cores on the same shaft (which they sell as a factory-assembled dual-core motor)... always, as far as I have seen, using two controllers.
I suggest asking Cascadia about this, both because they made the controller, and because their motor division has lots of experience with two Remy/BorgWarner HVH motor cores on the same shaft (which they sell as a factory-assembled dual-core motor)... always, as far as I have seen, using two controllers.