Can you ping it from other devices? You may want to contact their support.
Yes, the Switch can be ping from Every where even from the Observium Server properly. But just not able to add the switch into the Observuim Server.
I have contacted DC and they said it might block on the switch due to Rate Limit.
Page 598 https://downloads.dell.com/manuals/all-products/esuprt_ser_stor_net/esuprt_networking/esuprt_net_fxd... try setting a rate limit.