I took a quick look in to this just now since i did the original QA for the Extreme Prayer. As far as i can see it still works with the Holy Wrench, and it also works with Reverence aura. Both Rev aura and Holy Wrench also stack.
At level 99 prayer the Extreme Prayer pot heals 565 points, with the Wrench it heals 584 points. At level 50 prayer it's 320 points without, and 330 points with. No reverence aura used here btw. As an FYI though, Reverence aura does 10% of the original heal then adds the Holy Wrench bonus.
Are you going off your own in-game experience or just the wiki? My conclusion from looking into it is that the wiki is wrong. However, if there's a strange condition causing it not to work, then that's a bug that i'm not aware of and would need someone to give me some info on that.