. . . probably. Two coats isn't very much and if your Danish tung oil is watery thin it should mean that there is hardly any sitting on the surface.
I often French polish on top of Danish Oil but I have two 'rules':
Don't have it sitting on the surface.
Make sure it's thoroughly dry and hardened.
The Oil gives you one advantage. It pops the grain a little better than straight shellac. Actually it pops the grain better than virtually any finish out there, which has something to do with it's index of refraction.
Shellac on top of Oil is a close second best to Oil all the way. Shellac on top of Oil can violate the 'lean to fat' principle though. A hard finish on top of a soft finish can lead to crazing - the finish underneath moves but the stuff on top is too hard and brittle to move with it.
That's basically why Shellac on top of an Oil finish may be a bad idea. Thin enough and hard enough and it's not usually a problem and of course there are no adhesion issues with shellac.
