Any resemblance to any human or animal, living or dead, is simply coincidental and unintentional.
Or something like that. You get the picture, they don't mean to have the horses be another horse. (Except in the NTRA published game, in which point you can race the legend, it's fun and an exception) But general game play horses are not meant to be anything but fictional.
However, I am currently playing GI Jockey 3...and they are doing a bad job of hiding these real life horse replicas. For example...so far I have come across:
Lemon Syrup Kid
The Min Man
Go For Band
These horses are the same coat color, gender, and run under the same colors they did on the track. Yea, totally a coincidence. I'm just hoping I come across a super awesome bay named Cigarette or maybe a chestnut named Man O' Peace....War Sergeant vs SeaMuffin?