Deb in the forces isn't necessarily a problem, so long as it is clear that you're dealing with it and it's under control. If you bury your head in the sand or try to ignore the problem (especially if it gets to the stage of missed payments or CCJs etc) than it can be a problem that the chain of command can do little to help.
If your husband approaches his chain of command now, before it gets to a troublesome stage, they will help him and it will be done without judgement (assuming he has a good OC/CO, that is!). They won't blab to his fellow soldiers as everything will be treated in strictest confidence - just as they would with any other welfare issue.
You say he's away right now - is he due home soon or has he just left. If he's just left on a six month tour, don't leave it until he gets back. Seek advice from your unit Welfare Officer or SSAFA and start the ball rolling now. If he's due home soon, get it sorted as soon as he gets back.
As for redundancy - he shouldn't worry. I know it's hanging over everyone right now but redundancy is not decided purely on whether someone is in debt or not - it's a lot to do with cuts in certain regiments/corps v expansion in others and they're hoping that a lot of the next tranche or redundancies will come through "natural wastage" as people reach the end of their careers as well as people applying for PVR as they decide to move on.
My last warning: debt will become a problem if he doesn't seek help and if it becomes a problem, it may well escalate to a disciplinary matter and AGAI action. The fact you're worried about it suggests that things are becoming difficult to manage for you both, so please, please, please seek help now. It will lift a weight from both of you and will help you get clear. Also, your husband needs to be clear to his chain of command just how the debt was incurred - gambling, like other obsessive behaviour can be a problem on its own and he needs to be able to reassure them that he has that under control. Given that he's going to GA, he seems to be doing all the right things.
My husband is a serving officer and, believe me, he's seen and heard and helped with all sorts of stuff and I'm pretty certain your husband's chain of command will have done the same so he shouldn't be afraid to seek help if he needs it.
Good luck.