Is it safe to remove "rdmgrab" in Mojave
I did a bit of searching on this. I don't suppose you have TeamViewer, LogMeIn, VNC or another remote viewer installed? Chrome desktop anywhere?

This could be related to that?

See this other stack exchange post:

https://security.stackexchange.com/questions/71344/strange-tcp-traffic-on-mac-os-x-from-rdmd

Thanks,
Ed