S7horton,
I've been building and selling custom furniture of all types for a living for over forty years and have yet to have a problem using lemon oil, especially on veneers. Veneers can start to split when they get too dry regardless of the finish on them. I have veneered pieces more than forty years old with the original finishes that have been wiped down regularly that show no noticable change in the appearance of the finish. I would be more worried about getting the lemon oil on the cones and surrounds of the speakers.
I've been building and selling custom furniture of all types for a living for over forty years and have yet to have a problem using lemon oil, especially on veneers. Veneers can start to split when they get too dry regardless of the finish on them. I have veneered pieces more than forty years old with the original finishes that have been wiped down regularly that show no noticable change in the appearance of the finish. I would be more worried about getting the lemon oil on the cones and surrounds of the speakers.