Not sure how it is in NJ, but here in Va, after you take your underwriters test and get your license, you must be approved as an underwriter with an insurance company, not an agency, within 6 months or your license is no longer valid.  Around here, the big companies do their own thing and the agencies to their own thing, meaning, for example, Lawyers title has their own in house underwriters, examiners and closers. And agencies have their own people.  Though I am sure in some places, the main insurance offices use their agencies.

I would suggest, if your state requires a license, to get it and work for someone until you get familiar with the underwriting standards of your state and of the different insurance companies.  Each ins co has different requirements for their work products, wether a sale or a refi. 
But if you already underwrite, just give some of the ins company contacts you have a call and ask,  They probably would be more than willing to help you through the whole process,

Hope that helped a bit.