I think that is a fair substitution as far as getting the desired physiological benefits of the workout goes.
A couple of other thoughts:
- I wouldn't substitute a race for this workout if having a subpar race might make you doubt your fitness or otherwise have a negative psychological effect. Jack ramps the mileage down gradually over the last month, but the big taper really comes over the last 2-3 weeks of the cycle. So when you run this race, the effect of the taper really won't have taken hold and you will probably be racing on fatigued legs. Sometimes people pop good races under these circumstances, some times they have off days. I usually fall into the latter category, but that really doesn't bother me. But if it might bother you to see a 10k performance a couple of VDOT scores away from the VDOT score of your goal marathon pace, you would be better off not racing.
- If you are feeling at all banged up, I would skip the race in favor of the workout as the race will be more demanding. Not point in risking a marathon cycle in order to get in a 10k race.