I have zero issues with him keeping it... he carries the burden -- I show up and just fake through the gig.
This is what I think. Now, I am assuming that this guy is being a true BL and "investor" or "impressario" for the band, and that it's not a foregone conclusion that it's strictly democractic.
As a BL myself, I see this unexpected money and consider a) did I take a lesser pay for this gig to keep the band working, and to hit their minimums? b) Have I recouped my costs of putting this event together for the band? It sounds like he's paying for leads, costumes, etcetera, doesn't he deserve to get that back? c) I am not concerned if you are a sub or not -- you got the gig at an agreed upon rate of pay. If I pay you that, end of story. I have met my obligation to you.
If tips were not discussed, then it's up to the BL decide what to do with it. Also, when I'm a sub, I want to be asked back again, so I want to be on my best behavior with the gig booker, and that means not making an issue of such things -- particularly when I don't know his expenses.
So, having seen both sides, I am in favor of the BL deciding what should be done with it. But...read on.
If I knew the whole band saw the tip that was passed to them, I would probably talk to them about it since the fact they saw it raised expectations. I would say "guys, I did this gig for free so you guys could get your minimum pay and we could open up a new venue. So, I would like to keep the tip to give me SOMETHING for pulling this off". or "Guys, I foot all the bills for the band and get the same rate of pay as everyone else, so I think it's only fair if I get to keep the tips to cover my losses". If they balk at it, then I'm going forward based on a personality assessment of the people objecting.
If the guy is an entitled complainer by nature (I had one), and easy to replace musically. I'm going to assert myself and if he doesn't like it I won't call him again. He's on thin ice anyway as someone who complains a lot and takes my work for granted.
If the guy is nice about objecting, or in short supply musically (no other musicians can do what he brings to the table when I need a sub) then I would likely be softer about it, and use reason to help him see. Or I might pass it out to everyone evenly that time, but indicate that in the future, I keep the tips to cover my expenses -- and let them know what those expenses are. We'd sit down and I'd let them know exactly what is involved in running a band, and that showing up, getting paid, is only the tip of the iceberg.
Also, his reasons -- gigmasters at $200+ per year, his time spent booking, any costumes he paid for -- those are strong, valid expenses for which he should be compensated. I am surprised people consider them weak reasons. They are not -- those represent money out.
I find that if the band members get too demanding about what they expect from me as a BL, without considering my needs and expenses, I tend to stop doing it. And then there are fewer gigging opportunities for everyone.
There should be care and feeding of the band leader. Sadly, I find few people actually do that, so I have to look after my own care and feeding, and avoid situations like this if I can help it.
[Note,for years I was the doormat for the band. I would even say I wanted to spend coin on certain marketing efforts and can we take it off the top of the next gig? No one answered my email. I eventually told everyone that when I ask for input, and they don't answer, I assume they agree with what I want to do.
Eventually, I saw democracy doesn't work when everyone doesn't pull their weight, and am on the band leader as broker of musicians, without every disclosing total pay rates for the gig as a whole]