They are clearly used as different pokemon, complete with different tiering...just like Shaymin and Shaymin-S. That is the spirit of the Species Clause and I think we should allow multiple forms on the same team. It's not like we're still in gen4 where the Rotoms were all the same type and only had one move to distinguish them, Rotoms in this gen clearly cross the line of what it means to be "different enough"
If we use a "dex number/no hold item" specific Species Clause it would make a handful of pointless bans if we applied it to other aspects of our clauses. Shaymin, Deoxys-D and Deoxys-S would be banned from OU, and all the non-Washer Rotoms would be banned from UU (as well as Shaymin and D-D). If we use this approach then we're setting a precedent by saying "yes, we think Shaymin is the same pokemon as Shaymin-S" which I think is a silly thing for competitive pokemon battlers to say.
If we make Species Clause just form specific, it doesn't have any impact on our metagame.
So in short I think we should treat them differently, like we've been doing with tiering.
NIGMAN: JRRRR IS A SHIT
NIGMAN: HO ESLE THINK IT??