This is true... however, I'm not convinced that VBAC moms who choose an epidural do any worse, in general. Continuous fetal monitoring seems to be the most reliable indicator of UR (pain often accompanies UR, but usually changes to fetal heartrate patterns can be seen earlier), and that will be covered if you've got an epidural. If you wait until labor is well established (say, 6 cm) then more often than not it won't slow things down too much.
IMHO, it's simply a preference issue. Lots of VBACers got burned the first time they had an epi b/c it initiated the cascade of interventions (or, more often, was a part of that cascade, which started with induction of labor). So it's a case of once bitten/twice shy.
I actually know several moms who had epidurals and successful VBACs. Although it wasn't necessarily the plan for them, it's what ended up working best for them at the time.
My opinion: plan a natural birth, but go with the flow when it comes down to it -- if things aren't progressing fast and an epidural will let you get some much needed rest and let your body do its thing, this can be very helpful. With a supportive care provider, there's no reason an epi should change your chances of having a successful VBAC.