Question of relation between methodology and its subject area is quite generic. One one pole, every case is specific and deserves its own methodology. On another pole, nearly every case can be cast to any given methodology with more or less voluntary approximations.
If we use too many narrow methodologies, we complicate communication and mutual understanding between different stakeholders. If we use just one methodology, we may complicate transparency of models due to improper casts of real business objects to limited dictionary of the chosen modeling style.
As always, reasonable balance should be observed between two these polar situations.
In case of RPA, it doesn’t have usually too complicated workflows and falls relatively well into BPMN domain, which exactly targets this class of business automation solutions and interaction of business and IT systems.
In fact, role of RPA in terms of BPMN boils down to just one simple symbol substitution. RPA replaces manual BPMN tasks with script tasks representing RPA automation scripts.