He sure could be. So could BSP or Curtis Painter or Tyler Palko or Tim Tebow. We don't know because none of them have had legitimate opportunities in the NFL.
The problem is that given the instability of the Cards' QB situation as it stands now, IMO they don't need further "unknowns". We already have that with Leinart. My point is that now is the time to have backups who have experience.
Unknowns are all you're going to get!
It's not like we can go all and sign Drew Brees or Peyton Manning. Virtually all the QBs that have been available this offseason are either has-beens (Chad Pennington), QBs with major warts (Anderson), or unknown commodities (Charlie Whitehurst).
I'd rather go with the unknown commodity because at least if they have the talent there is a chance they'll flourish. Ideally we could have both, but as it stands now, most of the decent veteran options are gone.
And lastly, if Leinart doesn't work out with the way our team is, I seriously doubt Charlie Batch, Chad Pennington (who obviously isn't on the market now), etc. would really help. The NFL is a QB's league, and without a good one, you're chances in the playoffs are limited.