OP if you are very much informed with happenings around the Crypto space, you would recall that of lately, there have been series of hacks on discord so in that case nobody would want to risk their discord accounts and portfolio. If anyone refuses to send you server where they worked before, you would not blame them as they are being careful and cautious not to be get hacked or being a trap or medium to infiltrate other projects server.

I expect you engage or interview them to see if they really have the experience as they claim they do if you doubt their application. That would have been okay rather than demanding for what you know is not feasible.