As mentioned above, it is quite possible that "flight will credit perfectly to UA", but it is still, first and foremost, a VS flight, so both UA MP & SQ (depending on the details of their codeshare agreement with VS) will be well within its rights not to credit it, especially if a retro credit request becomes necessary. Furthermore, the OP would have no way to ascertain what the 'translated' SQ Booking Class would be before purchase and it may well end-up being one of the non-earning SQ Booking Classes (G/Q/V/N/T).

The airport *G benefits will, indeed, apply, as they only require a [physical] flight that is operated by a *A member carrier.