Well if the tx was accepted by the pool in the first place it would have to be running some custom software.  I assume it would try and relay it normally but it would only be accepted by peers that were following the same relaxed rules as itself.  I have played with nonstandard transactions in the past sending them through Eligius to get mined and it does seem that though they are accepted and eventually end up in a block that I do not see them get propagated very far elsewhere on the network before being mined.  I assume that it would work fairly similarly for transactions with fees below minimum.