One of my colleagues has done extensive research on DADT, and what he calls the "GUN" - the Gay Underground Network. Another colleague does research on military families, based on what they told me, NO. Under no conditions is it a smart move for a queer person with a family to join the military.
First - the military is very pro-family. It is in your best interest to get married and have kids in the military, it will boost your pay, your spouse and kids have opportunities available to you that they wouldn't if you worked most blue-collar jobs. This only applies to straight men who are in the military (unless women are married to men who are happy to be stay at home parents/work part time).
Second - the military is very anti-gay. Your family would not be recognized - none of the perks available to military wives and children would be available to you. Think life insurance, death benefits, pension plan, not just military housing or health insurance.
Plus, there are no guarantees. Your wife would always have something that could be used to get rid of her at any moment.
Last, it's very hard to be a military spouse. When their husbands are deployed, military wives are responsible for all of the childcare, household work, etc. It's like being a single parent for months at a time. The frequent moves from place to place make it nearly impossible for most military wives to have an established career, unless she can telecommute 100%. Yes, it's possible to have a job, but you can count on moving every two years.
Remember - you're a gay family that the military doesn't recognize. You can count on moving every two years and paying for it yourself - they'll move your DP's stuff, but single soldiers don't get to move their "friend and her kid" on the military's tab.
I'm very, very, very, anti-military (especially US Military) so I'll put that bias right out there, my brother is a reservist, my grandparents were military during WWII, I grew up in a military town. I have friends who enlisted, I have a high school buddy who was killed in Afghanistan.
If I were in your shoes and my DP was seriously considering joining the military, knowing all the stuff I outlined above, I would see it as a disavowal of our relationship and our family. If my DP was actually going to join the military, I would kick hir to the curb. I know that's pretty harsh, and I'm not saying you should do that, just to be clear.