Can a 220V US circuit have more than one 220V outlet, by code?
The code doesn't care if you say you're not going to use stuff at the same time, it assumes you will. 

I don't think it would be a code violation to have multiple outlets on a 240 volt circuit (though I could be wrong). The number of outlets is not restricted (at least not that I've seen), based on voltage.  

However, the conductors have to be sized for the load, and the overcurrent protection sized to protect the conductors.  So in an existing install, you'll be limited by the size of the conductors that are installed.

My advice would be to remove the dryer receptacle, or run a new circuit for the workshop. If you remove the dryer receptacle, you can extend the circuit to the shop from the junction box.  Then you have the option to go back to a dryer hookup.