You have to raise. Flatting shows weakness, as the odds of you having a monster are unlikely, since I'm not sure A2s is in your opening range. That leaves AK
and 33 that would smash this flop. An overpair is your most likely holding. You need to raise to chase out unpaired, overcards hands, at least to make it expensive for them.
Only a non-diamond 6-8 doesn't make you cringe against 4 opponents. Against 1 other player, you can "meh" an overcard. The 4 or 5 gives random A holdings a wheel draw, but that's unlikely to add anything to V's thinking, except add a small bit of equity. So you really only like 20% of turns in a multiway pot. (11/47 including the other two 9s)
If you get called in one place, you can probably get to showdown, but if V1 gets frisky, you might have to stack off with 2nd pair. Say you call, there would be about $270 in the pot, if V1 puts in a raise to $300ish, you would have to ask what he could have that smashes the flop, and its a little more likely for him than it is for you to have A2s (but not much). But really, if V1 re-raises, I'd be tempted to put him on a bluff. Thus, raising helps you make V1 make a mistake, while calling prevents it. Even if V1 puts you on 55-TT, its very unlikely for him to have you beat.
Also, you started the hand with 300bb, which barely considered "super deep". Is this a $500max buyin game?