"An Nvidia engineer" would actually be grammatically correct here, since the pronunciation of "Nvidia" starts with a vowel sound and not a consonant one. It's the pronunciation of the word that matters for a/an, not the spelling.
In case anybody was wondering, the official pronunciation of the word "Nvidia" is apparently "en-VID-eeyah" [1].
[1] http://international.download.nvidia.com/partnerforce-us/Bra...