LED driver configuration
Your instincts ("It's not typical in my experience...") are correct. That circuit won't work. The IRF530 needs 4 volts Vgs worst case, and that is simply not going to be possible when you include LED forward drops. 

However, it's not clear what your justification for doing this is. You mention that you don't want to "use inverse logic on the control point". If this means that you want to use a 5 volt signal to turn on the LEDs, put the MOSFET on the negative side of the current sources, with the source at ground. If you want a 0 volt signal to turn on the LEDs, replace the MOSFET with a p-type MOSFET, with source at +5. Either way will work.