Re: Any advice on using butcher block for bath vanity?
I think given the proper sealing and care it would work out. You must start with a high-quality glue-up. A year ago (on another board) someone had bought BB from lumber liquidators, and cut in a hole for an undermount sink, only to find that her "maple butcher block" was glued up from red oak with a 1/8" maple veneer glued on. It was never built to be cut, because doing so exposed the oak core. So get assurances that your BB is solid whatever lumber you choose. I think white oak, ash, maple, cherry or mahogany would be great in a bathroom. Stay away from red oak, it will stain if your finish fails and water gets in.
Use a finish like Waterlox, and put at least two coats on the bottom side, and use the recommended four coats on the top and edges, cutouts, etc.
Remove not the ancient landmark, which your fathers have set.