We just upgraded Netsight and we keep getting alarms with regards to an expired radius server certificate in NAC. We are currently doing proxy NAC hence I don't need to update it. Is there a way I can delete it as I don't seem to be able find that option.
Could it be that your are able to delete it in.....
NAC Manager > Server Information (3rd icon in the task bar) > Certificates > Update Server Certificate > select & remove Files.
I can't try it as I don't have certificates installed on my NAC so my menu is empty....
I see, great (for me) that Extreme implemented this feature 
You could delete it in the filesystem but I cannot tell you if this has no sideeffect. In the GUI you cannot delete it. I would recomed to renew it as selfsigned.
We started getting this alarm only after updating to Netsight 6.3, it was not there in previous versions. I can see we can update but wanted to see if there was a way to delete it completely.