Have you looked at the Environmental Query System yet? It uses the nav mesh. You didn’t say whether this was for a player or AI controlled charcter, but the eqs system works very well with AI behavior trees. You could have an eqs query find valid points within the nav mesh to roll to and then only if there is a valid roll to point within some [max roll to distance], then execute the sideways roll. Here is a link to the docs on EQS:
https://docs.unrealengine.com/latest/INT/Engine/AI/EnvironmentQuerySystem/UserGuide/