^Yeah, my gut feeling is that it's probably a joke/sarcasm/trolling. To me, it just doesn't make any sense, since I don't think that anyone took them that seriously to begin with. An accusation like that would probably make the company put the girls involved on haitus, and I don't remember any mention of conspicuously long absensces from that time.
If it's a joke, on the other hand, it makes a lot of sense to say that maybe Yuko was fed up with losing in the running events so she took something. In fact her struggles with the running events was played up for dramatic effect in one sports festival video from around that time. Any way I look at it, it just makes more sense as a joke than anything.
Of course, to quote the last US administration, "the absense of evidence is not evidence of absence". This is all conjecture, and I might be completely wrong. Though I'd think such a story would have stuck around in the fan community if it were true, just because I've personally never heard of it doesn't mean that no one has... (in other words I'm pretty close to 100% sure that it's not true)