Is there any new information on how the Syslog server Dev is going for The Dude?
How do I go about specifying an IP range to be Blacklisted?

There is no dude related development. We all can only be glad that the dude at least works somehow and mitigate the problems it has. Even those errors that are well known to mikrotik are not subjects to correction in reasonable future.

Is there any new information on how the Syslog server Dev is going for The Dude?
How do I go about specifying an IP range to be Blacklisted?

"blacklisting" is done inside ROS on the device where the dude runs.
Create /ip firewall address-list no-discover
and put the ip's you don't want to be discovered inside that address list.
after that :
in dude in the "Network Map" you want discovery -> settings -> general -> add the network you want to discover -> add the no-discover blacklist. It should be visible there.