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.
Now that becomes even more wrong since SQ partners with VS (and owes a 49% stake of it). Absolutlely no reason why SQ should not credit a VS codeshare on SQ as long as it is a milage earning class.