Unfortunately, college discounts do not apply to refurbished items as far as I know. Education discounts are year round, but sometimes they offer special incentives (i.e. the free ipod touch you can get now).
No, I don't believe that the educational discount applies to refurbished items; I imagine that the reason for this is that two discounts would then apply - and Apple will tend to apply only one at a time. However, the refurb discount tends to be pretty generous, in my experience, better than the educational discount (unless you include the additional incentives sometimes added on, such as the iPod Touch). The educational discounts apply all year, but, as buddyguyman points out, additional special incentives do exist at certain times of year (the obvious one being just before school/college starts a fresh term/academic year). Good luck and cheers.