Depending upon the details they could be kept alive in a herd for Wraith feeding. Various healing devices might reduce the number of Jaffa / Goa'uld required to feed a given group of Wraith.
I have no direct support for this opinion, so I'll work through a logic tree based upon the facts available in the show (I've only read one novel).
Can a Wraith kill a Jaffa / Goa'uld?
- A Wraith's feeding kills in seconds - less than a minute for sure.
- Symbiote healing takes many hours to days (depending upon the
severity of healing required).
- Therefore, "yes" a Wraith can kill a Jaffa or Goa'uld in not much longer
than the time it takes to kill a human
Can a Wraith "farm" Jaffa / Goa'uld for sustenance - meaning if allowed to live, could the symbiote heal the damage done by a Wraith's healing? In series, symbiont healing works by the power of plot (it does / doesn't do) what the writers need for a given story, but
- I feel that "yes" is more consistent with the TV series than "no".
- A symbiote enables the human host to survive trauma that a human
without a symbiont could not.
- A symbiote retards aging and allows the host to survive for many
hundreds, perhaps thousands of years.
- Meaning the Wraith could develop a "herd" of Goa'uld for feeding
How would a hand device or sarcophagus impact the equation?
- Hand devices are less powerful than sarcophagi but work faster
(seconds to a minute).
- Sarcophagi can heal most anything - including death in humans but
take hours to a day to work.
- My impression is that a Wraith could still kill someone being
actively healed by either of these.
- There is an episode of SG1 (Season 5, Episode 8, "The Tomb") in which a Goa'uld is sentenced to the
most horrible death his priests could imagine, burying him in a
working sarcophagus with a flesh eating critter. The sarcophagus in
combination with the symbiont try to heal the damage done by the
flesh eating critter - nice. The episode does not say how long it
took for the Goa'uld to die.
- Therefore, if the Wraith could get their hands on a sarcophagus, then
they could make do with fewer Goa'uld in herd to sustain the Wraith.
- But as the point in #4 shows, it is possible to kill them with
overwhelming the healing with many small injuries.