The purpose of the pool is to provide assurance to the merchants using the system that their transaction will be included in a block as quickly as possible (one reason for regional sub-pools).
AFAIK, I don't think a mining pool is necessary for this assurance. Once the majority of bitcoind nodes (weighted by hashing power) have the txn in their memory pool (ie, ca. 10 seconds after broadcasting the txn), the txn is pretty well confirmed (even with 0 confirmations)(assuming sufficient txn fees, but even with 0 fees it's pretty solid unless the txn is huge, like 2kb). If there is an orphaned block or two, the nodes will still keep the txn in their memory and hash it into the next block.
There was talk about having p2pool secure ~10second confirmations that it would include a txn in their next block, but I can't dig up the thread right now. Did forrestv ever comment on the feasibility of that? And speaking of p2pool, it gives out coin-base + txn fees, only charging a voluntary donation for development.
tl;dr. I don't think OpenPay needs a pool, but I may misunderstand something
edit: Here is the thread on using p2pool for 10-second partial confirmations:
https://bitcointalksearch.org/topic/m.1071988edit2: What I said isn't secure against Finney attacks, it seems =/