Locking hub question

I think so. Applying vacuum when switching to 4wd probably won't hurt anything in the short run but it could draw in contaminants past the hublocks' O-rings in the long run. If the vacuum line between the frame & knuckle is removed, you must plug the fittings. Open knuckle fittings will allow all kinds of moisture and dirt to accumulate in the bearings/hubs. Open vacuum fittings may confuse the vacuum system.

On my '02, I replaced the knuckle fittings with steel plugs (3/8" NPT IIRC) and plugged the vacuum fitting on the frame with a sheetmetal screw, and tossed the vacuum line that was in between.