Thanks Justin, I was able to use feathers-rest on the server and feathers-socketio on the client with the help of steal-conditional:
https://github.com/leoj3n/bitcentivez/commit/bce502921c9d49b6efab90fb48e4d841217ba516
However, although it works locally in development, I encountered the following issue when attempting to build and deploy:
https://github.com/stealjs/steal-tools/issues/1086
It seems steal-conditional causes the conditionally loaded files to not get included in the bundle. 
You can see the resulting error in the console on that page: https://bitcentivez.herokuapp.com/contributors
NOTE (to future self):
Here are some related issues that might benefit from this method of loading feathers-rest in SSR:
https://github.com/donejs/bitcentive/issues/97
https://github.com/donejs/done-ssr/issues/198
https://github.com/canjs/can-connect-feathers/pull/104