Technically Polite Whisper Wrath Extended is already breaking the license since Polite Whisper has none and is All Rights Reserved, but how the community handles licenses is slightly wonky.
It's not exactly explicit, but #1 in
UI Add-On Development Policy can be interpreted as any addon you pay for that isn't publicly available isn't allowed. If you paid $300 to someone and they released the addon publicly, it would be ok since you were just paying for them to update the addon, and it's still freely available.
Which means in order for this to be allowed, you need the original Polite Whisper authors permission for someone to redistribute the addon. Then you would be in the clear with someone being paid to do this.