Hello Chris,  There is a Rule from Exchange cartridge called "Port 135 And 445 Connectivity Test" which will provide similar functionality as DC connectivity Rule.  This Rule basically checks if those two ports on monitored Exchange server/s are reachable whereas DC connectivity Rule just runs a ping test for monitored DC/s.  Hope this helps.
Trying to copy the dc ping rule and point it to the exserver topology object.  But its not working because there is not property for the excserver topology object called isreachable like there is for the ad_domaincontroller object.  how can i create that property object?
Copy DC connectivity rule and make it s a exchange connectivity rule