What are the current options for implementing server push with a dotcloud app hosted django app? (similar to socket.io on node, channel api with appengine or apache comet)
The options are pretty much the same on dotCloud and on other environments. I.e., if we check Django / Comet (Push): Least of all evils?, we learn that websockets won't play very nice with Django, but that asynchronous WSGI should be possible with http://code.google.com/p/evserver/.
I would personally use evserver using a dotCloud custom service; it should be fairly simple to support, and will provide clean long polling.
You can also use websockets, if you're not scared by django-websockets (or find some other way to do it).