I added some of those names in the "Preferred 'Name in Game' Characters" game option and tested it using the mod Prepare Moderately. Without Humanoid Alien Races active they appeared consistently in the first 100-1000 rerolls but with it active they never show up, even after 10000+ rerolls
The backer pawns that only have a custom name and always get a random backstory show up normally even with Humanoid Alien Races active
The backer pawns with unique custom backstories from this list never appear in the game: https://www.reddit.com/r/RimWorld/comments/vhj088/list_of_all_backers_submitted_unique_pawns/
I added some of those names in the "Preferred 'Name in Game' Characters" game option and tested it using the mod Prepare Moderately. Without Humanoid Alien Races active they appeared consistently in the first 100-1000 rerolls but with it active they never show up, even after 10000+ rerolls
The backer pawns that only have a custom name and always get a random backstory show up normally even with Humanoid Alien Races active