Hi Cyrus,
Thank you very much for your post.
I am not sure how your POS works, but it should not cause an issue with PL (You will have to test it all unfortunately what would mean purchasing a single short term licence - remember there are no refunds). You, of course, will not be able to sell the PL custom product types either as I doubt your POS knows them.
It is very hard to advise you on this as we do not support 3rd party services.
I am very sorry that I can not be of more help.
Pavel