The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. - that is a very low psi #. - - so some food for thought - - even if you have a cap that allows twice the typical pressure relief - there is no way a properly installed hose and clamp won't hold back 30 psi. - barb or not. I won't say this as a "it IS this" but it seems to me the barb is simply a tool or point of reference, it sure makes it easier to see or feel where the clamp needs to go and it undoubtedly adds to the sealing capability of the piece, but I don't think it's the defining factor in sealing the system.
