A 120/240 3-phase delta is fine; it suffers from a misunderstanding due to perspective. In the 120/208 Y, you have a central ground point, and all points out from that ground reference are 120 VAC and 208 VAC from phase leg to phase leg. This is not true of the 120/240 delta, where one of the 240 VA...

If you hold a license of the appropriate class, then yes, for Part 97.

If you don't have a Part 97 license, then it's legal until you get caught.

IT guy here, Engineer in deed. Extra class...