Heck, I'd be fine without the op-amp. How precise do you really need that current? It's a neon tube, it won't mind 10% here or there, and you probably need to calibrate to its scale or intensity anyway. A 0-5V DAC range, offset by ~0.7V, will get you plenty of linearity for the remainder of that range. A digital calibration would be pretty straightforward to eke out just a little more precision (down in the exponential range 0-0.8V say, bonus points if a temperature sensor is equipped, to cancel out Vbe tempco -- at that point, the op-amp is preferable though).
An R+C snubber on the open collector might be desirable in case of long wires potentially causing oscillation, both in terms of the neon lamp (a negative resistance device) and the transistor (making some manner of oscillator with its capacitances -- unlikely for merely a MJD340, but easily addressed regardless). Ballpark values might be, oh, 100pF + 1k?
Voltage and temperature limits might be desirable, but can also be solved externally with suitable caution (e.g. series limiting resistor plus tube; fault monitoring, maybe check that Vout is in nominal range?).
Tim