Hi Steve Joe is correct.....don't apply drywall compound to a joint without taping it. The reason is that even though those joints seem tight right now, they will not always be so (foundations settling, framing wood shrinking, wind loading and shifting, etc). If you apply compound without tape, 2 years from now you will have many small and perfectly vertical cracks running up and down your bathroom walls :-(
Now, the real challange (and what I fear has happended) is the original drywall contractor butted non-tapered joints together to achieve the flat surface over which the wall paper was hung. If so, ugh!! Tell you what, rather than my going into a long dissertation on how to fix such a thing, check and post back if this has indeed happened.