The easiest ways to make 29.97 from 23.98 are to:
render it in Final Cut Pro, by placing your 23.98 sequence within a 29.97 and rendering, or export, import, and rendering, such as you’re doing.
Use After Effects, which has a feature to add 3:2 pulldown, thus turning a 23.98 to 29.97.
But as Shane has stated, this is an unnecessary complication, especially if they are working with a quicktime file. It made some sense in earlier times when sound was editing to a 29;97 videotape as the only visual sync source.
The simpler the post pathway, the less chance of problems. How are you finishing? Figure that out, and work backwards to decide how to proceed.