i am pretty sure all frequencies between the two are compatible. but i have always heard that if it doesnt say sprint on it, sprint is not activating it. also vice versa with vzw. i havnt found one case of someone succesfully using the other carriers phone on their network.
its discussed in this thread:
http://forum.androidcentral.com/google-nexus-one/7379-nexus-one-sprint.html
the answer is basically no. sprint has to have phones (ESNs) in their database for the phone to work. When you try and activate the phone, it wouldn't work since sprint won't recognize the ESN. However, the technology is compatible.
Can you explain how the ESN is sent to Sprint? Is it straight from the hardware or does it go through the software first?