possible...
I've seen a 350 motor that ran well, and had vibration troubles,and we found it had spun 2 main bearings when we pulled the motor and oil pan,to change a leaky rear main seal !..the bearing froze to the crank and spun in the block's bore!..and it had decent oil pressure and didn't knock either!..

..so I suppose it is possible!--also,worn thrust bearing surfaces on the rear most main bearing can wear ,so can the crank where it rides against it,and cause excessive end play,that can cause vibration or knocking noises..
A faulty harmonic balancer can cause vibration problems too..as well as using the wrong one on certain engines,and the flexplate too..if you have a 400 small block or a 454,they use an externally balanced balancer and flywheel or flex plate..put them on any other motor and you'll have a nice cocktail shaker!..
A bent fan (if its a mechanical engine driven fan blade) can cause vibrations too,as well as motor mount misalignment,driveshaft angles,worn bearings in rear end or tranny/transfer case,etc..does it vibrate when parked as well as moving,or just when your driving it???...
