After 25 years I wouldn't be overly worried about him drinking again. Frankly at a certain point I think worries about relapse often serve as a distraction from actual, present day issues....it's almost as if it's easier to talk about fears of relapse than it is to talk about what's REALLY going on.
And it seems to me that what's really going on here has nothing to do with drinking and not, in truth, a whole lot about betting. It's about the sense you have that he's keeping something from you, that he won't talk to you about it and this is part of a long-term pattern of keeping you at arm's length. That's what I'd want to talk to him about, and I would absolutely not frame the discussion as being about his "recovery".