Welcome to FT!

No you can't combine the two to redeem a ticket. The only way I can think of is transfer VS to Hilton Honors, then to SQ... but you lose a lot of miles value that way.

In what class will you be travelling? If J on SQ, then you will have access to the SQ lounges anyway. If Y, then you might want to consider Aegean as the alternative *A airline to clock your miles to... as you attain *A gold much faster and will gain you entry to the *A lounges (but not SQ SilverKris lounge in SIN).