blanch after vacuum seal?
I don't think this will be such a good solution. You can try it, but it probably won't do what you want. 

First, there is the problem of temperature control. In blanching, it is critically important that your vegetables heat up quickly, and then cool down just as quickly. If you insulate them with a plastic bag, you are building a thermal delay into the system, and this will reduce the quality of the blanched vegetables. They will be mushier and have worse color than when directly blanched. 

The second problem is that you'll still get liquid inside the pouch. Blanching destroys the cell walls of the vegetables. The juices from inside the cells start leaking. And this will happen inside the vacuum bag too. So, you won't have dry vegetables in the bag, you'll have vegetables swimming in their own juice. Unlike the normal blanching scenario, it won't be diluted in water, but it's still probably not what you wanted. 

This doesn't mean it's impossible to do it. You can try and see if you like your vegetables better that way. Just make sure that you choose bags which stand up to rapidly boiling water - it may be quite hard finding such bags.