As long as you are not claiming them as your own products, or that the logo is derived from original work of your own, you should be fine. And you are right about others ‘designing’ logos, they are considered “open source”.
I’m not sure you’re right there Adam. Technically, the rackspace logo is copyright (maybe even trademarked) to Rackspace. This means that it cannot be used without permission and it especially cannot be reproduced in an unauthorised way, which in this case probably includes being redrawn in a different style.
By doing this, the OP does leave themselves open to legal action. BUT, if they are providing something good to rackspace such as increased sales or traffic, they may be happy to let it slide. Maybe. On a good day.
So really, the OP needs to have a look at their agreement with rackspace if they are a reseller) or at the rackspace logo usage guidelines (if they are a customer of rackspace) to see where they stand.
A logo is not open source, it always depends on how the owner allows reproduction of it.