Yes, medical marijuana legalization can cause an issue of drug company ethics, because they have to answer the hard question of whether they will become producers. Legalization poses questions as to what stance each company will take as to how their business will or won't manufacture marijuana, and with what conditions.
I do not think that the legalization of medical marijuana is an issue of drug company ethics. I think that it doesn't really have much to do with the other. I think that the only time it will, is if drug companies decide to synthesize a product to mimic medical marijuana and sell it for profit.
I think if a company recognizes medicinal properties in something and the fact that something helps so many millions of people, there shouldn't be any ethical issues involving it. It should just be recognized as the medicine that it is, and used by the people who really need it. Quite simple.
I do not believe medical marijuana legalization is an issue of drug company ethics. The pharmaceutical companies sell many drugs that are far more dangerous than marijuana. The pharmaceutical companies probably don't have any ethical problems selling these products. If they can make a profit they aren't going to have a problem with it.