As a DM I have no qualms with such builds, as I have used such builds in the past with other DMs.
I would in fact encourage it, because as a DM, I am not sure how well I would be able to control my own optimization tendencies, and to be fair I worry less about the class features of these classes and more about actual spellcasting of classes in general, as that is the real threat behind these classes.
But then again I don't DM 3.5 all that often, and if I did, it would likely be e6 Gestalt from here on out, or perhaps Partial Gestalt based on class tiers similar to that described in the Tier list thread.