Multi Crew in Single Pilot Helicopters...
Yes, sorry, if you refer to the Flight Operations Manual as OM you are correct.
There are different OMs published by the OEMs in regard to operations with optional equipment like hoist etc. and I thought you were refering to that.
Anyway, both pilots need to be rated MPO for multipilot operations and with PartFCL it is not that easy (cheap) to either convert from SPO to MPO, or to optain an additional MPO rating. Not impossible though and it depends largely on who your competent authority is.