Vox, First my assumptions... Your Dom/Dom relationship is Male/Female, Your relationship is permanent (as much as any other). Then, yes a surrogate mother is appropriate for your situation. Whether the surrogate was sub or not would really be up to you and your "other". I can see where this would be a good thing. For one, as you stated, you could control what they eat and do while they grow your child and you could be there for the entire pregnancy.
But for the reality side of the coin, finding a Submissive surrogate may be difficult. Women in the surrogate program are screened to make sure that neither they, or you will be damaged by the eventual separation from the baby, or when the surrogate leaves your family. That very screening process may make your wish difficult to fulfill.
Loving parents to raise the child are much more important that who actually gave birth.
And before anyone asks "Why a M/F couple?" I used that example A. because it avoids the traps of legal rights. If the child is wholly the product of the couple, then the surrogate has no legal rights to the child while a "birth mother" would retain certain legal rights. And B. Vox made it clear that this would be "Her" child as in Her egg (correct me if I'm wrong).
As for the original question...No. I would not have a sub carry my child just for the sake of having one, but I would use a surrogate if necessary.