You will get JW's answering all over the map.
(1) Can one be a genuine Christian without being a JW?
They will say that this has been possible in the past, but God is directing people to Jehovah's Witnesses in these last days. Still, they may feel that isolated people here and there could be genuine Christians just waiting for JW's to find them.
(2) Can one be an "exemplary" JW without being a genuine Christian?
I imagine that sincere JW's recognize that there are JW's in good standing who do the right things for their own selfish reasons.
I personally find the first question rather presumptious. Asking if one can be a genuine Christian seems to imply that such a thing exists, while other beliefs would just be wrong. The same person searching for genuine Christians would assume that genuine [anything else] are living in false beliefs. Instead of looking at genuine Christianity as a truth, I can look at it in a way where "genuine" means living by the tenants of the belief. I personally think that virtually no humans genuinely live by Christianity in the fullest sense. Maybe the one known as "Mother Theresa" did so, and a few others, but most are not really willing to live their life fully for the benefit of others and be content with "sustenance and covering" or whatever the non-JW translation of such things are.
The second question: Perhaps millions of JW's are exemplary JW's because they attend the meetings and turn in recruiting time.