I moved some individual add-ons that were installed in the user folder to my workgroup. Softimage continues to see those add-ons as installed under the user folder, not the workgroup ?
PS. Installing shaders to a workgroup, is it the same as installing ICE compounds to a workgroup?
eX-SI 
yes, a historical limitation which make NO sense and should be fixed! 😉
Can you move add-ons which were installed as a general user, to a workgroup ?
Yes. Do it with Windows Explorer…just move the whole Addons folder to the workgroup.
I moved some individual add-ons that were installed in the user folder to my workgroup. Softimage continues to see those add-ons as installed under the user folder, not the workgroup ?
PS. Installing shaders to a workgroup, is it the same as installing ICE compounds to a workgroup?