I run compression on all of mine and they seem to work fine. The links that dont have the hardware compression seem to peg the CPU pretty hard though. I wouldnt suggest compression without the aim at over 700k or so.

Im not sure this is simply an SNMP problem. I have the same problem on my Cat 3550 but have noticed that if you do a show int for the VLANS in IOS they also show no traffic

You can also tell your router to do a per packet or a per connection load balance with the command ip load-balance at the interface level.