The Belius/Velius issue happened because in Japanese, there is no V sound (well, there is, but it's never used) - they use the 'b' sound to substitute whatever word has a v sound in it.
A lot of the espers are original creations that are influenced by the zodiac signs. There ARE, however, many of the characters from Final Fantasy Tactics, similar to Velius. There are also enemies from other Final Fantasy games as espers, such as:
Exdeath, Holy Tree of Judgement (Final Fantasy V), Zeromus, the Condemner (Final Fantasy IV), Mateus, the Corrupt (FFTA), high Seraph Altima (FFT's final boss), and more.