I know nothing official, but my initial response would be that it depends on what year the PNM is. If the PNM is a sophomore or higher, doing deferred recruitment... i.e., already enrolled at a different school, then no I don't think promoting your chapter would be considered dirty rushing. However, if the PNM is a freshman and not technically enrolled in any school yet... then in might be considered dirty rushing.
Please don't let this into any sorority girl's head though- we already have enough trouble at my U with agents
We don't need nearby schools/chapters teaming up and "not-dirty-rushing" each other's PNMs.