Don't know about "standard practice," but I try to keep alcohol away from any wood.
Alcohol isn't going to hurt wood -- it evaporates very quickly and there isn't anything it can do to wood that will hurt it. Well, if you submerse it in tub of alcohol and leave it soak there, that wouldn't be good, but you could say the same for water, gasoline, chocolate milk, etc....
Here's the big caveat: if you've got a shellac finish then you've got to keep alcohol away from it, as it will dissolve shellac. Shellac is applied by dissolving it in alcohol. Very quickly upon application the alcohol evaporates, leaving behind a film of shellac. Millions of wood articles have been finished in exactly that manner. Alcohol will not hurt the wood at all.
I am no fan at all of applying any kind of oil to finished wood -- I just think it's unnecessary and I dislike the slick, greasy feel it leaves behind. To clean the skin gunk off my fingerboard I use alcohol -- it's very effective and it leaves behind no yucky residues.
After-thought: I have no idea how alcohol reacts with any of the blackening dyes that may have been used on a fingerboard. Does that stuff come off?
Yet another after-note: I've just consulted my copy of Flexner's book on wood finishing and I see my lack of experience with nitro lacquer has betrayed me. It seems as if alcohol will in fact dissolve lacquer but, according to Flexner, not very well on its own. The overall point is the same, though: alcohol may pose a danger to some wood finishes (namely, evaporative finishes like shellac and maybe lacquer), but not to wood itself.