Sorry, I seem to have missed this post.
I run a 'cluster' of Rspamd servers and on the second test server I do have Clam A/V running as a service and I'm going to be removing (or rather disabling) the amavisd & clam A/V services on the live server. As I just have a private mail server those services never caused me a problem as Rspamd reduced the load on my server by about 15-20%
Thanks for your feedback.
I'd be interested to see how you get on with getting the metrics into Prometheus, I was thinking of using that myself but haven't really had the time recently do any investigation.