The requirements are that you have a background in firearms. That doesn't mean you have to have been a police officer, or a Navy Seal. From what you stated your background would meet the criteria. The idea is to teach the basic knowledge, skill, and attitude necessary to own and operate _____<-insert type of firearm here.
If NRA instructors only came from professional shooting backgrounds then there would not be a boyscout merit badge program at all.
Some of the best trainers I know never where military or professional police officers. Just like some of the best shooters where never a Police Officer or former Military and some where. Just like some of the most painful courses I've sat in on where from guys in the military or Police Officers and vice versa to Civilians. I don't believe in that whole well I was X therefore I'm qualified to do this.....I'm a put your money on the table guy and show me what you got! I'm not trying to stereotype one category of people I'm just saying most people get what they put into it or how they come to the training, and training comes from individuals and how they like or dislike what they are doing not just a credential hanging on the wall, and just cause your taking the wild west shooting academies uber tactical pistoler course for engaging unwanted rattlesnakes, your still taking a course from an individual instructor
If you come with the know it all attitude (happens a lot) you may not actually learn as much as you could. Even if I don't agree with something in the course I'm going to do it otherwise, why am I paying or using my time to attend the course? The best example I can think of is from one of my mentors who once told me he was at a course for professional development (firearms related) my friend has a tendency to write everything down. In this case he was copying everything the instructor was saying. The instructor asked him on a break if he really liked what he (the instructor) was teaching, my friend said "no in fact I disagree with about 90% of it but I'm putting it in my tool box to be possible used at a later time".
Some of the high level IPSC shooters come to mind, as well as SASS and olympic shooters.
Doesn't matter what walk of life you came from in the professional field everybody has a weakness. Trust me if you ever become a instructor trainer in any field you will understand this real quick.
I actually had a guy come up to me before a Instructor trainer course (which I was teaching) and said. Hey I'm your 1911 guy if you want to know how to shoot a 1911 just let me know! There are ways of dealing with such people, my method was giving him the section on single action revolvers. He had no idea how to operate a S/A gun but since he was military he had no exposure to S/A revolvers, but as an NRA instructor you are expected to know how to operate/use all the platforms in a certain discipline. The point of this was not to embarrass him, but if somebody comes across with the know it all attitude I'm going make for DARN sure they learn something in my class! Nobody knows it all. In fact I learn tons from my students when I'm sitting in class teaching an Instructor level course. The day this ceases to happen is the day I probably no longer am producing a pulse.