Yes, according to the rules, you have to be a gnome to be a cleric of Gond. On the other hand, many people don't even know that's a rule (probably including many of the game designers), and those who do tend to think it's stupid. You should ask your DM.
When the pride domain was printed in Spell Compendium, there was no explicit list of which deities offer it. When it was originally printed in issue 323 or Dragon Magazine, there was such a list. It's on page 65, if you have the issue. Otherwise, you can take my word for it that Gond is one of the deities that offers the pride domain.
The newest printing of divine disciple is in Player's Guide to Faerun, and it doesn't give a bonus domain.
If you DM sticks to the rule of only gnome clerics of Gond, you could be a cleric of Ubtao. He has "chultans" listed among his typical worshipers, which is a human ethnicity (Races of Faerun, p106). Counting an aasimar as a human isn't any kind of stretch. Though most of the aasimar in Faerun are from in or near Mulhorand, which is pretty far from the Chult. That could be a sticking point. Oh, the character is already in play. Nevermind