Q:Can the R-3W be used on an ungrounded 3phase application?

A: Yes the R-3W can be used on an ungrounded 3 phase system but you still need to hook the ground wire to an Earth ground. Please see page 14 of the attached installation manual for correct wiring. 

https://cdn2.hubspot.net/hubfs/477905/Grace%20Eng%20R-3W-INST_sm2-5.pdf