:agree:
If the CAD never engaged, you would be alright, and no, it wouldn't be 3wd. That's only if you have a spool or welded the front.
By why take the chance? If that CAD somehow happens to engage, you're going to break something, and it's not going to be something cheap and easily fixed. If you have to swap the rear without changing the front at the same time, take the front shaft out to ensure you don't accidentally crack your T-case in half.