I purchased standard 6 panel hollow interior doors and one door way is much smaller. Can I use sliding barn door hardware to hang this other wise standard hinge door?
Depending on the exact sliding hardware you are using, it should be possible. Hollow core doors usually have a solid wood frame along the edges, though how far into the core this frame extends may vary.
If you are using hardware like that shown below, you would need to make sure that the brackets attached to the wheels are anchored into the solid wood frame at the edges of the door.
It may not be ideal but I have made barn doors out of hollow core doors by simple 'easing' away the moulded layer (of one side of door - at top) and inserting/glueing wood blocks inside the hollow space where your hangers will be bolted. Then simple glue it back together. The blocks should coincide with the thickness of the doors wooden frame (between the two moulded sides).