Ok, so this is what i believe to be the case. I've actually been seriously questioning myself about this, but i can't think of anything solid enough to change my mind:
For basic sound post, frame rates don't really matter. If they send you a session with burnt in timecode, you really should match your session's frame rate to that of the video so your session TC matches the burnt-in. Apart from that, the only thing that should make you think about session frame rates is when you're linking up with other machines, especially video decks.
Here's why i believe this: Sound doesn't have frames. It has sample rates, but that can only affect the length of your audio if you transfer it from one SR to another without compensating for speed (pitch and length). In Pro Tools, this compensation is automatic. When you bring in your movie file, Pro Tools will play it at the correct speed, regardless of the session frame rate. To do otherwise would take some hefty processing power, and give you a jerky, stuttered image (i'm pretty sure). Pro Tools uses Quicktime to play video, and Quicktime will know at which speed to play the video. You can set your session to any frame rate and all it will affect is the TC ruler and output TC - never the actual speed of the session.
Of course, it's always a good idea to use 2 pip/end sync pips, to make the audio lay back easy and verifiable. Sorry if i'm not that clear, it's a friday afternoon thing. And like i said, if i'm wrong, i would be grateful to be pointed in the right direction.