You're correct. That endpoint call is a) for MX devices only and b) somewhat confusingly named.
I've gone over the API docs, but the only routing-related items I see are for the MX. I checked the getDeviceSwitchPorts call on an MS350 to see if perhaps the SVIs might get listed there, but that's only physical ports on specific switches in the stack.
I am not, in fact, finding anything related to l3 switch-based routing on the Dashboard API? And no OSPF anywhere at all...