you say the spa is "within" the pool - so you really only have 1 body of water - so a second pump is not needed.
Edit - If that is not accurate and you have separate suction for your spa and pool (2 bodies of water) - You only need a dedicated pump for the bubbler if you wish to operate the bubbler when in Spa Mode.
If you set it up to tee it off or your existing pump you will only be able to operate the bubbler in Pool Mode because the bubbler returns water to the pool. In Spa Mode you only draw suction from the spa so if you returned flow to the bubbler you would drain your spa over some lengt