Not sure about if snmp is the problem.
afaik with my WLC5500 I also had problems to collect the configuration via PI.
I needed to set the ssh timeout from default 60s to ~240s. (snmp timeout is still default 10s)
https://supportforums.cisco.com/discussion/13046011/template-deployment-bug-prime-infrastructure-310
-> difficult to find the configuration: see last entry from powys