If you buy the rental in your name this will have an effect on your debt to income ratio.

Currently, working on debt removal (everything except the mortgage), learning the math, and breaking down deals. 

All non purchasing spouses obligations on credit are included in debt to income ratio of FHA.

This in theory would allow me to make more appealing offers on deals and eliminate a lender on the front end, when negotiating with the seller.

If debt wasn't a thing that favored personal ownership, the conversation wouldn't be happening.For the time being, you'll want to assess your personal risk tolerance, financial situation, and tax situation. 

Question for BP... would you DIY finish your basement, costing $20k on 24 months no interest financing and adding roughly $50k to your homes equity, or spend those hundreds and hundreds of man hours instead building your real estate business with an end goal of being able to leverage $50-70k to put down on a multi fam property without having to go $15k in debt to create equity, but having no guarantee you'll make it as an agent.

My question is is there a way to show a potential lender that in fact my fiancé does pay half so my debt to income ratio reflects reality?

First you could check to see how long its been judgements expire in 20 years or each state has its own statute of limitations depending on the debt. 

When it comes to accessing loans, a traditional lender will typically need to run the Debt-to-Income Ratio along with Credit Score to qualify you for a loan.

Are you debt free?