can I use advancedfm from the 3.5.3 feed with 3.5.2?
Probably. Give it a go (you shouldn't need to install any deps).
can I use oz-compat-libs from 3.5.2 with 3.5.3, will that fix the dialog problem?
Not sure, but again, have a go and see if it does.
whats the rule with mixing feeds in general?
The general rule is don't, however using older apps shouldn't cause too many troubles (in my limited understanding of versioning).
Si