This is long, so skip it if you dont have the time, but if my thinking is way off here then a critque of it would be even more instructive than my thinking through it was in the first place!
I lean toward calling, but you are somewhat squeezed, and if the limper has ever shown a limp/reraise then I could be talked into folding.
The OP asks "How could he limp with pocket QQs?". I think analyzing that question is very instructive. Sitting in his seat I think Seat 6 played this very well, and I'll use Seat numbers because pronouns get too confusing, but "he" and "his" are Seat 6.He is in Seat 6, so pre-flop he's got 3 players out and 4 remaining behind him, inlcuding at least one very aggressive player...a good opportunity for a limp re-reraise. An all-in reduces his Qs to a blind stealing hand, foregoing a steal attempt from Seat 7 or 8 or a limp or two behind him. This late in the tourney I hate to get only blinds from a very strong hand unless Im critically stacked. The main risk of limping (vs a standard raise) is that he lets the blinds in cheaply if 7 and 8 dont raise and an A or K flop...a 30% shot if an A and K are already out there and worth the risk imo.As it turns out he gets his raise, but there are only 2 players left, including the very aggressive raiser, whose hand he discounts, so he focuses on the Big Blind. He knows the Big Blind called the raise despite being squeezed and has to put the Big Blind on a minimum of a high pair (lets say 10s or up for computation convenience.), AK or a small chance of AQ. He cant totally discount the Big Blind having AA or KK from the lack of a re-raise because the Big Blind has seen everyone fold except a limper and an aggressive player, so slowplaying them isnt terribly risky. (In fact a re-raise from the Big Blind might very well be a squeeze play by the Big Blind on him, so the lack of a re-raise doesnt tell him anything about the chances of the BB having As or Ks)He's got position on the BB, so why flip a coin and re-raise preflop, again considering Seat 7 could have a real hand? His greatest risk in not reraising is a weak Seat 7 flopping two pair, trips or a set...less than an 8% chance, so he's still much more concerned about the BB.Now rags flop, and the BB bets $600. He's got to believe that BB would push with any overpair to the board except the ones that have him beat in order to shutout any overcard draws, so the $600 bet screams to him that the BB is either begging for a call with AA or KK or BB has AK or AQ and thinks they are either good or at least have 6 outs twice. A call of the $600 bet gives the BB proper drawing odds to those 6 outs. So in Seat 6 he sees himself behind in 12 cases (cut it to 10.5 losses with redraws to a set beating BBs possible As or Ks) and ahead in 24 (but the 16 AKs get cut to 12 wins with draws and the 8 AQs get cut to 7 with draws), so Seat 6 sees himself as a 19/10.5 favorite..call it 2/1. BB has 1700 left and the pot if he puts BB all in the pot is 3850, giving BB well over calling odds. So at the flop, even discounting Seat 7 totally (in reality Seat 7 actually constrains him somewhat) he knows BB will call a reraise with proper odds. Does he risk leaving himself with 100 or 200 chips now as a 2/1 favorite? Many in Seat 6 would just push here without thinking, despite the near certainty of getting called by you and possibly Seat 7. (Letting Seat 7 in for $600 doesnt hurt him much, since Seat 7 is either ahead after a miracle flop, is drawing to the same cards as the BB or flopped a small pair and is drawing to 2 outs twice and not getting near the odds he needs for that draw).Alternatively he can look at the turn, preserving 1900 in chips (an M of over 10 unless blinds are going up very soon) if an A or K fall and he's forced to fold. If a blank falls as it did and you push he has the same decision to make. I.e. he loses very little by not pushing now, and gains the information and opportunity to fold later if BB catches the card he is going to stick around for anyway.The turn is another blank and BB puts him basically all in but he knows he's the favorite, so he's obviously calling.