I don't see what's wrong with this!
I have two sisters. One of them is the MOH. My other sister is really not into the whole girly bridesmaid thing, but she still wanted to be part of my special day, so I asked if she would sit at the guest book table. She was extatic to do so. My little brother is FI's groomsman (so cute ohmygoodness) and my older brother is ushering. My MOH sister's boyfriend is also ushering. (he's been around for a while, so he's more of a brother to me now). My cousin is playing piano for us. He's the one who taught me to play piano and guitar and how to sing when I was younger, so it was very fitting and he felt honored to be doing so. He wont even accept any form of payment.
Honestly, these people are really happy to be doing these things for us. It's a way for them to play an important part of the day while also not needing to be in the WP. They all are so excited to be part of the experience and they don't feel that it's rude at all. We will be giving them thank you gifts (obviously) but I just don't see why everyone thinks it's so rude?