JBossESB doesn't have native support for SMPP, but it does support JCA. So why not do both? The benefits would be that you are potentially future-proofing your development. For example, in the event you need transformation, content-based routing etc. If you're sure you'll never need those sorts of things (or capabilities that we'll be adding in the future, such as compensating transactions over arbitrary protocols, JBI, SCA, interoperability with other ESBs), then you may not gain anything over JEE+JCA for the added complexity.
Without knowing your full architecture and where you're headed, it's difficult to say. However, what is certain is that if you stick with JCA you can straddle both worlds.