I don't keep TBs but I know you don't get hybrid shrimp from mixing TBs, so it's okay for people keep them together. As for the Blue Bolt part, I read a post somewhere yesterday that BBs are too new of a strain to breed true but the poster didn't know if that was true or not. This just a conjecture, but I think people have mixed TB tanks to save money and lessen the amount of inbreeding but have a higher chance of getting more Taiwan bees. For example, if you buy a blue bolt for $100 and want baby BBs in the next generation, you would have to mix it with another TB, but that would mean you would have to buy another BB for $100, making it a total of $200. But, it would be cheaper to buy one BB and one BKK for a total of, say, $140 instead. Now granted, the chances of getting BB babies is less if you breed a BB and BKK together, but I believe some breeders wouldn't care about a mixed stock. But if you want more BBs, then it would make more sense to buy two BBs.
This is just my guess so please correct me if there's any wrong information.