I often see a bunch of vehicles with trailers right after the bridge on the way to the Gore Put-in. (after turning off the trough road heading to the actual Gore Put-in, about 100 ft from the trough road, west side). I assume that these are fishermen with oar rigs and dories running the stretch you are talking about.
You might call some fishing guides in Summit and get advice from them. A quick satellite scout shows a few diversions but from 23,000 miles up it looks totally runnable. South West Paddler says it good to go class II and III:
Lower Blue River, Colorado
Have fun and let us know what you think of it
also check out:
lower blue again 9/22/07
Looks like people are heading up there this weekend, you should get advice from and maybe boat with them.