The "promotion" you receive by promoting someone that appears out of nowhere can be pretty negative. That promotion implies an affiliation, and affiliating your event with someone you haven't vetted isn't ever a good idea. Someone that doesn't do their homework and take the time to contact you in advance hasn't shown good business sense and that likely applies to other parts of their business dealing. A photographers other income opportunity may be taking "oops" pictures of women coming out of the water or changing at transitions at triathlon. That goes over great when your event is run by a Christian charity.
Most are basically amateurs, but there are some that show up with multiple photographers. Professional photographers that have event coverage experience will off arrange for infrastructure to be in place like finish bridges, scaffolds at certain viewing points, etc. They get the vast majority of the race participants. When the event and photography company work together like that in a away that involves expenses by both it not in the best interest of the event to promote competing photographers. That promotion may be prohibited by the contract with the photography company.
That said, the more the merrier. People spanned out on the course get a better variety of pictures for the participants to pick from. Done right it's great all around. I don't think it's too much to ask that people attempting to profit from an event contact the race director, in advance, and make arrangements. Five amateur photographers standing at the finish really don't improve the opportunities for participants. The RD should be able to find out what the photographers intend to charge and ideally all the photographers promoted by the event would have similar pricing structures. I saw one guy that had pictures of the Boston Marathon for a mere $100 each for a digital image. A race director that promotes a cost-prohibitive service will surely be on the receiving end of complaints.
That said, my advice to the OP remains to contact the RD well in advance, explain what service they intend to provide and what they expect in return. I don't consider that an unreasonable expectation and gives it everyone a chance to have proper coordination.
Showing up unannounced on race day and expecting announcements at the awards ceremony or putting flyers under all the windshield wipers of cars in the parking lot won't gain anyone brownie points. Neither will expecting a bunch of free services from the race director when there was no advance coordination.
WIth relatively low cost digital SLR cameras and services like smugbug everyone thinks they're a professional photographer. A medium size event could get a dozen or more requests to "do business". If you think about it, you can't practically work with all of them.