My first thought was that this is totally disrespectful, but then I read a quote from the funeral director:
"Phillips told the Saginaw News that a growing elderly clientele who can't leave their vehicles to make it into his funeral chapel led him to think of more creative ways to offer visitation for loved ones. He recalled one woman who left a nursing home to attend her husband's funeral but was too ill to actually come into the chapel.
"She would've got a chance to see him if we had this, so I knew we had to move forward," Phillips told the newspaper. "Considering the elderly generation that we service, so many people are afraid of funeral homes. So why not be able to do it from your car?"
http://www.newsmax.com/TheWire/drive-thru-funeral-home-viewing/2014/09/17/id/595215/
After reading what he had to say, I don't think it's disrespectful for him to offer the option (though I think it could be used by people in a disrespectful manner). I've known people who have had difficulties going to the funeral home or staying there for any length of time due to health issues, and for them an option like this might actually be beneficial. There may be elderly or disabled individuals for whom this would make saying a final goodbye possible. In fact, when an aunt of mine died, I wasn't able to go to the funeral home because of a medical issue that prevented me from ambulating and kept me pretty much couch-bound for a few weeks. I was able to get to the car with a great deal of difficulty, but navigating the funeral home we have in town would have been much too difficult. Truth be told, had this been an option, I probably would have taken advantage of it instead of skipping the viewing altogether, just to have a minute or two to see her one last time, say a little prayer, and say one last goodbye. There may be people, too, who are unable to go to the funeral home during the stated viewing times that would still like to stop and pay respects to their loved ones. I've had that situation, too - viewing hours were during my working hours, and I would have liked to stop and pay my respects, but I wasn't able to do so.
At least after reading the article, I think the funeral director offering the service is doing so with good intentions and not as some sort of disrespectful gimmick. It's not ideal, of course, but I can see that there could be situations where this is a nice alternative.