You can execute any command over ssh, and return the output:
$ ssh user@host echo "hi"
hi
You could use this to run rspec:
$ ssh user@vagrant-ip "cd /path/to/project && rspec"
The thing to bear in mind with this approach is that your shell's environment must be set up correctly to allow access to the rspec
command. Your mileage will vary depending on how you manage your rubies.
But you can set up a command in vim to execute this SSH command, and the output will be returned, e.g.:
:command VRspec exec "system('ssh user@vagrant-ip...')"