Yes, you can loan it to anyone. If the device is activated, the RCC will no doubt call you (or whatever phone numbers you put down when you registered the device). This is good, of course, since you may be able to provide additional info helpful to the SAR team, such as how many people were on the trip, their gear etc.

As a side note, awhile back I had the opportunity to chat with one of the watch supervisors from the Alaska Rescue Coordination Center (RCC) at Joint Base Elmendorf-Richardson (where PLB alerts for onshore Alaska are handled). He said that ELTs (from aircraft) and EPIRBs (boats) tend to have a higher rate of accidental false alerts than PLBs. For example a hard landing is sometimes enough to trigger an aircraft ELT. Likewise EPIRBS which are designed to deploy and activate automatically when a boat sinks sometimes do so by accident. So in some cases (where there is reason to suspect it may be a false alert) they will try to make a few quick calls to verify before requesting a full on rescue mission.

On the other hand, PLBs require several deliberate conscious actions to activate. On mine one has to release and deploy the antenna, which allows access to the button, which then must be pushed to activate. Because of this, PLBs tend to have a lower rate of accidental false alerts. For this reason, the RCC is more likely to immediately request a rescue team to launch.