yes, it is definitely a good foundation. you learn bedside manner, you learn the basic vitals, you learn advanced vitals, your exposed to use of blood pressure meds, sedation meds, tons of meds (if...
to put things in perspective. I am a respiratory therapist, my girlfriend is an ICU nurse. An RT may have less to do with one patient vs. a nurse. But RT's have more patients than an RN. RN's work...
as far as being an RRT/RN, i doubt there is any such position. Unless you were a transport RN that held responsibilities for a mechanically ventilated patient. You can implement RRT skills as an RN...