SLAs are processed by OOTB standard agent rules. You don't need to configure anything explicitly to process SLA rules even if they are in branch rulesets.

The agent that processes SLA events uses the access group of the operator who created the assignment as its security context. Therefore:

1. If the operator had the intended branch on their ruleset stack when the assignment was created, and
2. If the branch is still on the application referenced by that access group when the SLA is processed by the agent:

... then the SLA in the branch will be run by the SLA agent.