If you think about it, a three phase load is made up of three single phase loads that work together to make advantage of the 120 degree phasing of the source. Each load of a three phase load, taken by itself, is indistinguishable from a single phase load.
Given that phase B is the high leg, adding 240 volt 2-wire loads to A-B and B-C will shift load off the A-C 120/240 side of the delta.
Nothing in the NEC encourages or discourages this placement of load on a 120/240 volt 4-wire delta.
The first thing I would wonder is what the local PoCo's method is for sizing the transformer(s) that supply phase B, the high leg? Do they put the smallest possible can(s) on the pole?