We are on Clarity 13.2, and wanted to know if this is compatible with Exchange 2013?
I don't recall any specific issues with compatibility between Clarity and mostly any version of Exchange.
Clarity is just a sender of SMTP mail, doesn't receive, and doesn't directly integrate in any other way.
So even if you did have a problem in a specific setup or configuration, it should be something that can be worked around by adding another mail gateway/proxy between them. Clarity would send mail to the gateway, the gateway could forward to Exchange, and then they'll be delivered from there.
But I doubt you'd even need to go that far.
The only problem I have run into is some Exchange Systems (administrators) do not configure it listen on port 25. We use Office 365 which wants authenticated SMTP (TLS 1.2) over port 587.
I built a little SMTP listener on port 25 and forward to Office 365 on port 587. The other option I used was a email service which would except SMTP on port 25 to forward the email.