The official OXM magazine says:
Recruit Packs will help you flesh out your arsenal, but it's probably worth saving for the better Reinforcement Packs. Rare weapons make a big difference in battle, and you'll also have a better chance of unlocking new characters like the surprisingly cute Volus Adept. Unlike in the world of football stickers, duplicate items aren't a problem – get the same gun twice, and it will merely upgrade the original weapon. If you've already unlocked the character on a card, you'll get training instead, giving that class a whopping XP bonus and unlocking new appearance options.
How do you unlock this race, or how rare is it?
Best Answer
As of the Retaliation DLC there actually is a Volus adept for multiplayer along with the DLC's content. I believe it is unlockable like the other classes via random items but I'm not sure of the specifics yet.
(Earlier answer retained for posterity; in the base content no Volus Adept existed)
There's no such thing as a Volus Adept in multiplayer.
As you can see from the list of Multiplayer objects from ME3, this class/race combo doesn't exist (note the "secret" Battlefield 3 character IS in the list):
The magazine was probably trolling or wasn't familiar with the race names, I assume they're referring to the Asari adept. It's been noted in the series that the Volus are terrible ground troops in low-pressure environment (eg anything a human can survive in), and there's never been a Volus in combat in the whole series, so it's extremely unlikely they'd implement one.
In addition, the only mumblings of a Volus Adept are in reference to this exact magazine piece, so I'd say Successful Troll is Successful.