Any reason not to set up Exchange 2013 with the iApp?

I would recommend using the latest version of the iApp as outlined in the deployment guide: https://f5.com/solutions/deployment-guides/microsoft-exchange-server-2010-and-2013-release-candidate-big-ip-v11-ltm-apm-afm

Also, make sure you have DNS configured since the Exchange monitors are based on the FQDN of the published Exchange service.

If all else fails switch to TCP or ICMP monitors so you can verify that Exchange is operating successfully.