Cheating is going against the rules of something (in this case sport) to obtain an advantage. So if there's a rule that says you can't use any PEDs, then yes, that would be cheating.

But as to whether or not something like you described should be against the rules, that's a tougher question. Sometimes injuries are related to the player's performance, how they play the game, in which case being forced to miss time because of it is part of a whole risk-reward schema, and reducing the risk side of the formula using PEDs sounds sketchy. But lots of injuries are just random, luck of the draw sort of deals, and would it be unfair if the player sped up the healing process, if it didn't affect the actual in-game performance? There's definitely an argument to be made that it's not unfair at all, since in the end we're still measuring the in-game performance. But you couldn't allow it for some types of injuries and not others.

And career numbers play into this as well. In most sports, a player's overall career performance is considered when deciding how truly great that player was. Someone could have two or three incredible seasons but then be affected by injuries and never do much else, and they would not be considered an all-time great. Would improved healing help those players reach their natural potential? Or shoul the player's natural stamina, resistance to injury, and physical/mental longevity play into their career numbers and their overall long-term greatness? Is the player who does better than average for 20 years without major injury better than the player who is phenomenal for five years and then flames out due to injury?

I think you could call it either way. However, there are some theoretical similarities between PEDs for strength and PEDs for healing. In both in-game performance and healing, there have been a lot of advances in the past 20 years that don't involve drugs at all. Equipment science, training science, injury prevention science, it all plays into both things, making the average modern athlete better in pure objective terms than the average athlete of yesteryear, without having to resort to PEDs. So allowing them into one part of a game (healing) but not into another might rub me the wrong way a little.

If it could be proven that a healing PED had no effect on performance, that it didn't help the body heal back to a stronger than natural level for example, and if a sport ruled that it was okay to use them, then at the end of the day I probably wouldn't complain. But the chances of a sport ruling in favor of such a method are probably slim, so for now, going back to my original definition, I'll have to say that yes, it's cheating.

Good question, though.