It would more then likely be the Washington County Simulcast. Allina RF's is still paged out by Pierce County, but it does sound like in the future, Allina will be dispatching for them fully.
Allina RF is dispatched 100% by Allina dispatch via 800 mHz. Pierce County (who takes the 911) will take the information and forwards it to Allina for EMD and pre-arrival. Pierce Co only sends the page to alert those who might be monitoring like Law Enforcement or if Fire is also dispatched.
The ambulances can receive 800 Mhz well but portables have issues. They are reported to be looking at doing a "mobile repeater" for potables.