To begin: Using the dcr files and running my own Habbo version 14 hotel was approved by Dutch staff member Jet back in 2009.
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Best TwixTX,
Thanks for your mail. As long as your hotel does not advertise on the official Habbo, we will approve.
We hope with sufficient informed.
Translated from the mail.
Edit 5/17/2012
Content removed: A thread on another forum has proven that retro server are still not ok to use. Maybe even when Habbo allows you to keep the retro, but I doubt that.