Have you heard of someone denied to visit an inmate from a criminal record of one misdemeanor possession of Marijuana over 2 years ago and thats it?

Yes, that is the baseline rule for every visiting approval - people with a felony record are immediately removed from consideration. BUT, that is not always the end of the road. You can (and definitely should) write a nice, humble letter to the warder and "appeal your case". Don't dwell on your former charge or when it was, but more importantly how you have a plan to help the inmate to not re-offend. To help them become a good citizen and have a successful re-entry. Wardens can overrule the ruling, but you are going to have to convince them it's a good idea.