It should be a non-issue, if you think about it,that's exactly the way most companies operate. You have the router at the ISP connecting to a router onsite, that may connect to another location, that bught backhaul a link to another location.
As long as each segment is independently addressed (different nets/subnets) it shouldn't be an operational issue. FUNCTIONALLY, there are some architectural concerns regarding traffic loads, latencies, capacities etc....
FWIW
Scott