There is a very good reason why "generalists" avoid Blood Bank and transfusion medicine - it's complicated and you need a lot of specific training to do it well. Even today, with a significant level of automation, a warm body is often needed to interpret results and give recommendations. And then add the fact that there is a seemingly endless list of "exceptions", "equivocal", "indeterminate", and other levels of results that confound even a trained (SBB) person, let alone an "every other weekend, third shift" employee.
Cross-training is a must for very small, low volume facilities. No question. However, once work gets to a certain level of complexity and volume, institutions should seriously consider having dedicated staff.
I don't know how "generalists" manage to maintain their legally-required competency levels.