Re: motor or equipment circuit ?
You could probably argue that it is a piece of equipment (appliance) and provide a circuit based on the nameplate. But in reality if you use 125% of the FLA, will the breaker hold? If this is truly a "custom" piece of equipment, is it UL listed, and does the nameplate comply with the NEC? If not, then I would play it safe and treat it as two separate motors, or at the very least a piece of multi-motor equipment. Are there 2 points of connection, or a single terminal box, like on a multi-compressor roof-top unit?
Also, don't they sometimes want to run just exhaust or just makeup air, in which case you might provide separate branch circuits to the motors? Most of the kitchen hoods we design require separate circuits, and they are run off of VFDs for optimal control.