After much research and trial and error, I was finally able to get my Cisco CIVS-IPC-3520 camera to stream to ZM. I wanted to share with you the settings:
I'm streaming H.264 from the camera. I also set the camera to ONVIF mode (under basic network settings) and turn off SessionID.
Source Type = ffmpeg
Maximum FPS = <leave blank>
Alarm Maximum FPS = <leave blank>
Source Path = rtsp://<username>:<password>@<ip address>/StreamingSetting?version=1.0&action=getRTSPStream&ChannelID=1&ChannelName=Channel1
for channel 2, it's similar:
Source Path = rtsp://<username>:<password>@<ip address>/StreamingSetting?version=1.0&action=getRTSPStream&ChannelID=2&ChannelName=Channel2
enjoy!

Note: This may work with other Cisco cameras such as the 4500.