As much as the media portrays him as Gandhi, Ray isn't the pinnacle of morality he's portrayed to be. Couple that with the fact that he is retiring at the end of the year anyway and what did he have to lose by trying to get back on the field? Nothing will happen to him by Sunday so worst case scenario he gets suspended next year, he won't be playing anyway so it's a pointless penalty.
I think he probably did use the deer antler spray. Professional athletes go to extremes to stay on top of their game and in peak physical condition. Lewis suffered a severe injury this year which kept him out for a good part of the season. Given that his team had a shot at going to the postseason and Super Bowl, which they are, I'm sure he used whatever means he could to get back to where he could play.
Since there is no absolute science behind this deer antler spray, there is no way of being sure. And if the man tore his triceps, shouldn't he be allowed to use whatever method of treatment helps him get better? Anyways, "performance enhancing deer antler spray" does not sound like something many professional athletes would be anxious to get their hands on.
While I wish I possessed a crystal ball to provide me with all of the answers, sadly I do not. I cannot say either way definitively if Ray Lewis used deer-antler spray. While it would not surprise me, due to the generalized acceptable of performance-enhancing substances in professional sports leagues, without hard evidence or a confession, we can never say either way conclusively.