Sure, but the software provided by one of the data integration vendors could work in both an ETL way, and an app integration way. You're then using the same piece of software to achieve 2 very different end-goals with presumably some level of improved supportability/providing more business value. If that's good enough; then excellent. If not, then that's fine too.
Saying that ETL/App integration are instrisnically a different class of problem to each other doesn't seem right, but then I'm just a programmer.