I currently maintain 11 accounts, each ranging in function from industry to combat. As it costs me nearly 3b per month to plex them, I tend to be very judicious when evaluating my need for a new pilot. Certain dedicated alts, such as an orca, have never delivered the type of returns that I would need to justify a new account. In order to recoup my time and isk investment into said orca pilot, I would have to mine at a level that is, in itself, somewhat counter-productive as there are numerous avenues with much higher yields than mining. Multiple accounts can be integral in the upkeep of corporations and POS networks. My invention and production cycles allocate 4 accounts, each with 3 pilots, in order to keep 120 lab slots in constant rotation.
If I were to throw my 2 cents in on your proposed plan of action...pushing a month into an orca on a PVE-oriented caldari pilot is not going to yield the sort of returns you would see if you just spent that month training the skills to benefit your primary role. If your hulk pilot is already fielding t2 lasers, you probably have the flexibility to cross train that into something without adversely affecting the progress of the mining itself simply because a hulk pilot lacks the open-endedness of a combat pilot.
My litmus is generally looking at my pilot and asking "Does he generate or justify 275m per month?"