[Dave]

I don't know for sure, but the veneer may be mahogony.

As for an alternative method of patching, wood putty may work, but it will be very difficult to match the grain & will likely stand out like a sore thumb. Since it's a curved surface on the front / top, I think putty would be likely to crack or flake off. I think a veneer patch would be your best bet.

The gap on the top is probably due to expansion & contraction of the wood. Since it's not loose, maybe just screw in a couple of braces to the inside of the cabinet to prevent further separtation, and fill the gap on the outside with wood putty. It doesn't look like a big gap, so it shouldn't be too hard to match the color with a little stain.

Dave