There's a re-veg thread in my signature if interestd.

The yellowing is normal, but no...they will not support the re-veg process. Adding some CFL's for side-lighting (veg or flower bulbs are ok for this) to promote new growth closer twords the base of the plant does help, though. (during the last week of flower)
I do this for my sativa doms, especially after a couple of re-veggings. My indica doms. don't require the side lighting, as they generally stay shorter, and usually get enough light to promote new growth twords the base.