I remember in the past when we had some outside collaborators, they were checking out from Windchill, without going through Creo.
The problem was there was a miss match in the iteration of the files.
For example the Creo file is say A.1 in your workspace and you check it in. Windchill now says it A.2, but the Creo file hasn't changed. If you check it out without using Creo, when you bring it up Creo's going to see it as A.1.
You need the workgroup manager to make that change when you add it to your workspace.
You just asking for problems. I'll bet this is why PTC took this ability away.
David Haigh