Is IRFD 014 an appropriate FET for switching an array of (about 40) UV LEDs?
Is there are strong reason for using that part? 

For simplicity, I would use a part specified with an Rds(on) for a Vgs of 4.5V, or lower. Typically the datasheet is much simpler to interpret.

Further the part is clearly specified by the manufacturer to work in that region.

There are quite a few parts which are specifically rated at 4.5V or below, though a lot of them are Surface Mount Devices. Is there plenty of space? If through-hole is important, it might be easier to get a physically larger package, like an IPAK. 

If this is a one off, or small volume system, I would make a 'no-brain' assumption, to make life easier, and, at least, double the required current to get a minimum device current. For small volumes the difference in part cost is likely a small fraction of an hour of my time. Hence it isn't worth designing something close to an edge which might use time later to check and debug it.