This incident and its reporting are leaving me with more questions than ansewrs. Unless I missed something, there is no mention of when the tests were run. It appears it was in Nome after the race, but how long after? This article states "high levels" of the drug were found (and high  is not defined). If so, was the drug administered just before the test (and after the race), or was it administered earlier in a very high dose to begin with? In the first case it would not have affected the dogs' performance, and in the second it would multiply the chance and severity of side effects (which don't seem to have appeared). 
In any case I'm not sure Tramadol would be anyone's first choice for a "perfomance enhancing" drug, and drugs, KNOWING the dogs will be tested?