Orion was originally a hub and spoke monitoring system and then along came additional polling engines where you could place an engine at a remote site to source additional monitoring. But an even better option is to use IP SLA monitoring from router to router checking site to site performance. Although IP SLA was developed for monitoring meshed VoIP traffic, it's also really useful for checking any mesh traffic. You'll need the Voice and Network Quality Manager module to use this functionality. Take a look at SolarWinds.com > Products > Network Management > VoIP and Network Quality Manager for more detail.