Technically the chromecast isn't hooked up to a specific device. It is a link to all devices through wifi. So as long as a device is hooked up to the same wifi then it will get the chromecast icon on supported apps to broadcast the content to the television. So in short yes you can have 2 devices hooked up.
You just can't, of course, have them both casting to the same Chromecast at the same time. (But 2 phones can be casting to 2 Chromecasts on the same LAN at the same time.)