Kobe on steroids? Doubt it. Steroids for basketball players doesn't make much sense.
However, Kobe on HGH, or any other basketball player for that matter - I wouldn't doubt at all. HGH speeds up recovery and helps with injuries. Kobe being the competitive maniac he is, I wouldn't doubt he'd look for any edge to help with his age. Plus the NBA doesn't test for it.
Can't just sit here and accuse him tho, I'm sure there are other players on it. Kobe's still going strong because he's an amazing basketball player, skillfully and mentally. Jordan was just as good or better than Kobe at 34, but medical advancements have improved so much in 20 years. I'm sure MJ would have gone to Germany, and I'm sure LeBron will go when he hits that age.
It shouldn't be that surprising that Kobe's still dominating, he's that much better than the competition, regardless if he loses a step and isn't as athletic anymore.