I dont think so as it will be too easy to hit if buy bonus result is counted with its base bet. If it does count, to complete the challenge then players need to win $5 (base bet of $500 buy bonus)*150 = 750 so it will be like winning $750 from $500 = 1.5x payout only. And if it works like that, I'm quite sure the challenge has been claimed already as getting 1.5x from buy bonus is easy.
That doesn't what I mean, if everything works such as what you mentioned obviously it would be too easy to be done. What I mean is both min bet amounts and multiplier are counted from the initial base bets, not based on how much the cost of bonus buy for the min bet counts.
For example a challenge with min bet of $10 and have to hit x150 multiplier, then I do it through bonus buy (the cost would be $1000) in the end I got results of $1600, do you think it would be counted as the valid one? Indeed it's just 1.5x ROI if we look at it from the bonus buy cost but I took decent risks as well.
Simple logic, no sites will offer $5,000 as the reward for such easy task and multiplier is something that we know as the winning result divided by the amount we spend/risk for the bet.
From the beginning there are no insane sites that would offer that much for such a thin multiplier