Here's the problem with "atonement" healing from my point of view: You have 3 atonement spells. From those 3, 2 are on a CD and hence haste does very little to them. The third, Smite, is a relatively weak heal. Also, getting more haste will not necessarily buy you more Smites. For example, suppose that with your current haste amount you end up with half a second left before Penance comes off CD. At that point you have to either not cast another Smite or delay Penance. The only way haste will make a difference in that would be if you can get enough haste to actually finish the next Smite cast within that 0.5 second. In other words, you would be looking for haste breakpoints to reach that would nicely line up the smites with the Penance&HF CD. In my opinion any plan that advocates haste should do these calculations, otherwise more haste in and of itself doesn't really boost your atonement healing any more.
To put it simply, you want to cast penance and holy fire on CD. Haste will only benefit you if it does in fact allow you to fit one more Smite in between those CDs. So first of all you would need to compute those breakpoints so people can aim to be right above them. But even in that case, given how little healing Smite does compared to that Penance, that extra Smite is very unlikely to offset how much weaker that Penance will be with the sacrificed Crit&Mastery.