According to the OP, the operating airline is SQ, even though the flight number is Virgin. SQ is a UA partner, so it seems that the OP should get miles. Of course, I only have experience with the converse: my mother flew BKK-TLV on a Thai flight, but operated by El Al... she received no miles since the operating airline (El Al) was not a partner. But since the OP's case has SQ as the operating airline, it seems like miles would accrue...