2 issues:
1) as the others have said, if you can make a reservation with pts (banked, current, borrowed or transferred in), then you can rent out that reservation. (you cannot actually "rent points" - that is how we talk but it's a misnomer - you can only "rent" a reservation).
2)
using pts from a december 2010 UY to book a reservation in june 2011 is not borrowing pts in the first place. those are actually current year pts because they are being used in the dec 2010 UY - which is the period from dec 1, 2010 to nov 30, 2011.
it's a common misconception but UY has nothing to do with when a
DVC member calls to make a reservation. to make a june 2011 reservation, you can use banked pts from dec 2009, current pts from dec 2010 or borrowed pts from dec 2011...