I had dwarf hairgrass in my tank when it was fully planted. It took off, did super well with only 2 watts/gallon (I got some desk lamps and bulbs and clamped them to the tank, nothing fancy at all), nothing else. My stocking was a little high at the time so maybe that had something to do with it. It took over most of the foreground of the tank within a few months. Then I ripped out all of the plants, but a few clumps of hairgrass remained. I only turned on the lights occasionally and it is still alive almost a year later, but it obviously isn't thriving.
So, the point of my rambling is that for dwarf hairgrass to thrive and take off you might a bit of a higher tech set up (and some luck), but it will probably survive even in a low tech set up.