There's no magic formula to getting into a TT program in NT. So many qualified people apply for each spot that you're never guaranteed admission; there's definitely some luck involved. That said, of course there are better or worse things you can do to make you qualified in the first place. An MDiv from Truett would put you at a disadvantage because of its academic reputation.
But I don't think the MDiv degree as a whole is disadvantageous.
I'm currently in the NT PhD program at Duke. I'd say 60-70% of us (in NT, specifically) have MDivs; I'm one of them. Granted, these are almost entirely MDivs from big name schools. Especially if you're interested in teaching in a Christian context, I will always recommend the MDiv (at a big name school) over another master's degree to prepare you for a PhD in NT. Why? 1) Cost: I have no debt from grad school, thanks to scholarships and generously funded internships. 2) The length of program: it gives you more time to build relationships with letter writers. You will have more course requirements than other M* students, but the extra year means the number of electives even out anyway (at least in my program). 3) Job opportunities: lots of people who think they want to do PhDs don't even end up applying. Interests change, the reality of the job market sets in, etc. An MDiv will prepare you to do more than just get a PhD. If it's at all appealing to you, you can become a pastor, work at a non-profit, be a hospital chaplain, etc.
Re: your chances of getting in to a big name school for an MDiv: I can only knowledgeably say this about Duke, but, yeah, you'll get in. Seminaries across the country are bleeding applicants right now. Admissions rates are incredibly high. Worry instead about being competitive enough to get a good scholarship.