I'm a lemon oil guy too. I have mostly maple necks and I use it on them also. I wipe the whole instrument down with it as a cleaner and then I polish it up . I have one bass, one 40 year old guitar, and one 140 year old mandolin with rosewood fretboards and they see lemon oil periodicly. If the frets are a little gunky, I use a soft tooth brush with lemon oil and follow up with some 0000 steel wool.
In a very dry environment a lot of bad things can happen to a rosewood fretboard. I knew a guy who had a beautiful old gold or orange label ( mid 60s) Gibson 335 that had seen almost no playing time and had barely a mark on it and the finish of the instrument was good, but the fretboard was a mess. All the inlays were popping out, there were gaps around everyone of them, and the grain of the entire board was so open you could stick your fingernail right in the cracks. This thing was stored in its' case for years here in Michigan where it's pretty humid, but it was in a house with a poor humidifier and it ruined an otherwise beautiful instrument. I'm no expert, but with the rosewood as F'd up as it was, it would seem that the finish would also be dry and cracked, but it wasn't. Anyway, the thing I took away from this experience was, take good care of the rosewood.
Rick