Yes, offsetting a surface is usually a good way to see if that surface would shell correctly. (I say usually because that has been my experience, but it is always possible that I haven't seen the particular cases where that isn't true.)
If a solid won't shell, I try offseting all of the faces and then cut out faces until it will offset, narrowing it down to the "bad" faces. I'll then try offsetting the bad faces one at a time to see if they will offset a smaller amount. This often gives you clues as to where the problems lie. If I have the freedom to change the faces, I will try to fix them so that they will shell. If, for whatever reason, I can't fix them, then I will try doing the largest offset that I can, then try offsetting the offset to get the final offset or a closer offset until I eventually get to the final offset. If that doesn't work, I will try splitting the face so that I can offset part of it, then use a Fill Surface to fill in the gap. Sometimes you just have to fill in a large gap with a Fill Surface with guide curves or one or more Boundary Surfaces, using 3D Splines to approximate the shape you need.
As Alin mentioned, some parts will shell, but won't offset, due to some advanced error correcting tools in shell that don't exist in offset. That means that if it offsets, it will probably shell; but not nessisarily the other way around. Also keep in mind that it can also be the transition between two surfaces that causes a problem with offset/shell, so make sure to offset all the surrounding surfaces as well.
Another good option for troubleshooting shell is to use the split command to split the model into multiple bodies, and then only use the shell command on one of those bodies.
Thanks a bunch for the insight.
I'll read through the advice and see what we can do.