I know you are asking for the opinion from luthiers, which I am not. However, I have researched this a bit over the years, and have been around a variety of instruments for my entire life.
There is nothing wrong with oiling, but as has been suggested by a luthier in this thread, it doesn't make the wood impervious to humidity changes. Even Alembic, who recommends perhaps the most extreme oiling regimen I have heard of from any manufacturer, states it is ineffective at preventing fluctuations:
"You may notice that the first time the humidity takes a big swing that the fret edges may protrude over the edge of the fingerboard." Despite recommending, you "saturate" your board, and let the oil soak-in for a minimum of thirty minutes, their boards still expand / contract with humidity changes. Oiling should help mitigate the effects of humidity fluctuations on your board, but it won't stop it completely. Even a lot of finished necks/boards are still affected to some degree, and will need truss-rod tweaks after long periods in arid conditions.
Interestingly, the obsession with oiling seems tied mostly to electric instruments (wind instruments get oiled a lot, but they also see humidity extremes far beyond what a guitar sees under normal use). Everyone else is more concerned with actually keeping their instruments in a stable environment, and oiling as a secondary measure. I guess humidifiers are equated too strongly with hollow instruments, with an unfinished interior. People seem to think it is just to prevent tops from cracking, or don't consider it at all. I think people would benefit more from a case humidifier, or, if displaying their instruments, a room humidifier. I oil my boards very rarely, and I don't have any issues. When I do, it is more for aesthetic reasons, than anything. I have seen well-oiled ebony boards shrink. On the other hand, I have seen "dry" ebony remain perfectly stable when kept in a humidified case.
+1 on the Watco Danish Oil that Clement recommended.
