Will ESB and BPMS from different vendors work well together?

Last week I was talking with a colleague about ESB and BPMS. Vendors are offering BPMS with ESB features, but the company where he works will evaluate BPMS and ESB separately.

I think it is hard to define where ESB’s responsability ends and BPMS’s responsability begins. Besides, what kind of requirement will guarantee that ESB and BPMS from different vendors work well together?

Standards could be used for ensure the interoperability of ESB with BPMS. But how to be sure the vendors really follow the standards? For example, if a requirement states that the ESB registry must be compliant with the UDDI Version 3 standard and another says BPMS must be able to discover services at an UDDI Version 3, when ESB and BPMS are from different vendors do you really believe they will always be compatible?

Choosing BPMS and ESB separately can bring the best of two worlds, but you must be careful to avoid a gap between the platforms.