[whpalmer4]

No, an action can only belong to one project.

You can make a link that you can paste into the notes of another action (or any other text file on your Mac) which when clicked will open OmniFocus and take you to that action. Select the target row, do Edit->Copy As Link, paste where you want it. If you had an action like "buy ladder" in projects "paint ceiling", "replace chandelier", "fix roof", you could put links to the other "buy ladder" actions in each project so that you could go tick them off when you bought a ladder and free all of the projects to move forward.