Nothing specifically, but I might remember we had sometimes in the past a problem with this, I did not test it recently thoug
However, normally you want to avoid problems by keeping the things as simple as possible.
Having the disk image in the dropbox is already adding some complexity to the setup, adding the mount point to the dropbox too adds one more layer of complexity and things tend to fail when to complex.
If the user folder path, ie. Dropbox path to the mountpoint folder is exactly the same on each mac, then it should work in theory.
The best is to test it with some uncritical data and see if it works. Make sure though to lock the folder on all macs except on the one you are using the folder with, to avoid disk image syncing problems.
Let me know how it went,
Rgds
Zsolt