I think quarian's at least once had hair... or an analog to hair (they have some avian features in limb build, foot, and hand structure... so why not go the extra mile and say they have single filament feathers akin to down, it'd look like hair but have a different texture.)
I actually think a lot of evidence for that is actually in the design of the veils... the curly pattern in Tali's reminds me of curly hair, especially in close up shots, while the hex and line pattern on some of the other quarians seems to evoke hair draping down around their shoulders... Not only would the veils be a means of customizing their suits and making themselves more identifiable but also a means of suggesting their appearance beneath the suits.
So Tali probably has curly hair by that standard... I photo-shopped an image I found online towhat I thought they'd look like without the helmet... where did it go...