You are allowed to report anyone you wish (though I would recommend reporting in good faith), at any time. It doesn’t mean Blizzard will agree, nor will it mean that a possible punishment will deter the behavior.
It’s a solid question, but not likely one that you will get a definitive in here. I believe the intent is for the player advertising to be part of the actual purchased run, which is still possible in this scenario. But as always, there’s a lot of grey area.
Best advice we can give is to report and let Blizzard sort it out.
You don’t have to worry about this, especially if you are reporting in good faith, as I suggested above. This is something that happens when groups conspire to squelch players, not when someone is reporting a possible violation.