Re: Propagating arborvitae under lights
Arborvitae roots easily, so I suspect you'll be successful. Only catch might be that indoor temps could prod the stems to grow before there is much root to support them. This is why warm bottoms/cool tops is the propagator's motto.
Any way in which you could keep the room cooler, then apply some bottom heat under the trays, would improve the setup you've described.