It is clearly allowed, but should raise the 'amateur' flag, along the lines of taping wirenuts. Nothing wrong with taping wirenuts...but it should make you wonder if the wirenuts were properly applied.
I agree to a point but IMO one should consider the whole installation before passing judgment.
I run a lot of MC and still some NM, I often end up with both these cables in raceways.
A very typical situation is the following.
I have to run a circuit from a panel in an electrical room across a suspended ceiling then down a wall to utilization equipment.
Many of our customers only want to pay for cable for the concealed portions but want raceways in exposed areas.
I run a raceway out of the panel through the exposed electrical room until I get into the concealed suspended ceiling, if the other end at the utilization equipment is not going to be fished I run raceway there as well.
Now I pull a cable through the ceiling, use a change over fitting at the raceways and pull the cable through the raceways.
I can see no point in adding splice points at each end simply to avoid pulling the cable through the raceway.
It is code compliant, it is safe, it is economical and leaves less terminations which are generally the source of problems.
