Actually, come to think of it, I'm still not sure about this play. Here's my thinking:

Two Js on the board; one 9. Before the reraise on the turn, nothing about it makes Jx more likely than 9x. In fact, 9x is more likely since there are more out.

Assuming MP3 was likely to have the J from the rerasie:

2 Ts + 4 8s = 6 outs. 13% to come on the river. $3 into a $27 pot means that if I can make ANYTHING on the river when I hit, this is +EV. The presence of QT screws this up, but that goes back to the argument about raising in position preflop.