Correct, the Members code included in the first run editions of FFXIII on PS3 had three different functions:
- Registering FFXIII to your Square Enix Members account
- Registering the Asuran Armguards
- Offering access to the FINAL FANTASY XIV beta
Here's a knowledge base article on the topic from the launch of FFXIII.
This code is the one we're referring to, I hope that clears it up!