The release notes suggests it should work.
https://www.cisco.com/c/en/us/td/docs/net_mgmt/cisco_network_assistant/version6/relnotes/ol32368.pdf
What model is SG300 is it?
What error do you get?
Also, see here:
http://community.spiceworks.com/topic/738385-trying-to-add-sg300-s-to-cisco-network-assistant-6-1
You may need to create a new community.