In the book's description for Gamba (Suezo / Hare) the description says something along the lines of "There used to be a white Gamba with a red eye long ago."

Is this a reference to the Brillia Suezo from Monster Rancher 3?

Yes, the descriptions were written by a US employee who left fairly soon thereafter to return to his native England to try and start Tecmo UK. His name escapes me right now. -This drives me nuts because I can hear his voice when I read those descriptions.

But, yeah, referring to other games, especially MR3 because it's the past was an easy way to get it written up fairly quickly.