It's not super easy to help you on this one since I don't have a SCOM environment running with 3par hardware available, and also since the latest versions of the 3par MPs are not indexed in systemcenter.wiki.
However I don't really see how the discovery could be running "from the management server" while enabling "the collection server" to receive traps? Could you explain in more details how it's done/how it's supposed to work?
It would make more sense that the discovery is running on the collection server, which seems to be confirmed by the fact that you have to manually specify the management server action account in the runas profile. As you said, if the discovery was running on the management server, it would use that account by default...