Your friend decides that he will get married in the summer during the height of vacation time, and gives people only 6 weeks notice. Any friend at all would first consult the people in his wedding party to check on conflicting dates. This IMHO, would be the very first thing to do as a common courtesy.

So it's clear to me that your friend obviously doesn't care how his impetuous actions impact anyone else. That said, I would certainly bring up the fact that you have travel plans, and ask if they would consider alternate dates, or consider having the wedding in Vegas.

JMHO