I've got a customer who has a UX5000 and we will be swapping it out for a SV8100 soon. The question I have is the customer is using a UX Call Analyst server. Will this run with a SV8100 or will it need to be upgraded also?

I would think not but call Trivium (make sure to have version) to check (I believe the SMDR comes out the same). I would be concerned about the licensing on the processor and how it relates to your Call Analyst. Surprised you are going 8100 and not 9100.

I Have a Call Analyst doing remote site over Aspire/UX and SV8100's mix.

We have a 8100 on the shelf from a customer who backed out on us. It will be our last 8100 I would imagine.

Depends, There are some issues with fancy stuff (DID campaign) I have ran across, but 99% of the stuff will work.