It seems as if Tenno can use Transference to an extent while in cryo. Rell was different and I think he was actually in the Harrow frame or that his bodied died, but his mind was still in his frame. At the end of CoH we destroy Harrow so Rell can be free and die. The transference in our Orbiter does not put us in stasis. The Tenno don't seem to age and stasis seems to weaken our ability to use Transference. There is a lot we don't know yet such as if Tenno need to eat, drink, if they age at all, etc.