That snoop should be showing you requests by MAC address too. ie you should see your server you are trying to boot's MAC appear in the snoop output on your jumpstart server.

If you aren't see anything like that, then the problem is one of:
Bad network in between
Broken network on the jumpstart server
Your target server isn't sending ARPs properly

check network port has a link, check switch, check you don't have a crossover cable where you shouldn't or vice-versa.