personally iv always had trouble with dwarf hair-grass but that may be down to it not liking my water iv tried it in high light and low light, with CO2 and without the best i got it to grow was in high light with CO2, however it survived in low light as well, but didn't spread or flourish, i think to get it to grow well you need CO2 however some people have had success without, if your looking for plants which carpet there is a wide range out there.
iv found that Sagittaria Pusilus is fairly easy to grow
blyax japonica is is quite similar to hair grass, however i dont think it likes liquid carbon (testing my memory here been away from the hobby for 3 years)
if you have CO2 then theres hermianthus callitrichoides
if not you can always use moss's to form a carpet, id recommend java and weeping moss as there easy to grow
there are other carpeting plants out there as well, it depends what effect you want to have.