Young is currently working his way back from a hamstring injury and was able to run on Monday. The former Titans starting quarterback was on the inactive list during the Philadelphia Eagles 31-13 win over the St. Louis Rams on Sunday.
In the Eagles week one win, Vick was hit 11 times by the Rams, which highlighted the weakness along Philadelphia's offensive line. If Vick does end up on the sidelines for any stretch of time Young will clearly be the team's first option. But there is almost no use in having Young on your roster, because if he does play it will be behind the same porous offensive line that Vick has to deal with.
Vick is superior in every way to Young. So expecting him to step in at any point and be better than Vick was this weekend (83.7 quarterback rating) just isn't smart. Yes, the Eagles will get much better performances out of Vick this season, but I don't think that if Young were to step in and start he could possibly be any good.
There are plenty of better backup options available, and the only value Young has is as a handcuff to Vick, and even his value in that role is pretty low. Especially because of his injured hamstring. While he may be healthy enough to be active in week two, he will certainly be slowed by the injury for a while. That means if he does see time he likely won't be able to move around, avoid the rush or scramble as well as he usually can.
The bottom line is that if you're expecting to get anything out of Vince Young fantasy-wise this season, you're just fooling yourself. There are better options out there to fill out your roster, even if Vick ends up injured.