It just occurred to me that there is no incentive other than being a good beta tester to report serious (and less serious) exploits.
What if, depending on its severity, reporting an exploit would give you in-game rewards? There is just no other way to motivate players, I'm afraid.
(All of this can obviously be fine-tuned)
Rewards for very serious and hard to find exploits can be even giving the player the 500,000 caps bunker base and additional 100 skillpoints to one character.
Big exploits can be rewarded by leveling a chosen character to 21 via GM cheats (if there is a command to add exp to players, that is) and a chest full of BG, SG, EW ammo. (The equivalent of 200,000 caps)
Normal exploits are still important so the reward could be 150,000 caps and a few CA mk II.
Small exploits, which do not really unbalance things but annoy people could give the person a second tent or some other small reward. And 50,000 caps.
That way even the smallest of exploits, if found, will be tempting to report, especially if this player does not find it overly useful and would rather some caps or is greedy for items. And big faction-level exploits need to offer huge rewards to make people want to betray their friends
As a means of preventing a flood of reports of would-be exploits that in fact are features, anyone who makes a new exploit report and wants a reward should attach his character name. If the report is either good or bad, a GM will approach the character in-game and ask if they made the report. If they say "yes" and it is a good report, they get showered with rewards. If they say "yes" and it is bad, they lose a level and get killed :p