Mo, along with many top runners, is not clean. He is clean by WADA's standards however. Yet, it is undeniable that many of the top runners to push the limits as to what is legal. Not to mention all the other stuff AlSal makes them do and has available for them (ranging from strength training, underwater treadmills, cryosaunas, etc.). They're smart enough to not set foot into illegal territory. Until WADA decides to say "no" to a bunch of supplements or abnormal ratios that are actually allowed, then he'll continue to pass tests as will many other runners. If all everyone could use would be running and running alone, then WRs and WLs would be just a tad under what we see people run in college.
So is he clean? Probably not. Is he "WADA" clean? Most likely. As a result, it is not cheating since it is allowed. He is just taking advantage of it.