right, so those aren't actually giving people Hive accounts though.

Those are liquidity pools. Exchange tool.

The "b" in the name is similar to "swap.Hive" on the Hive-Engine. Basically, they have a big pile of Hive and HBD in an account, you deal with them, they send to your recipient, and broker the transaction between the sides.

So its a way to exchange and move the currencies around, or send a payment to someone with a hive account without making one, but it wont let you do any "hive things" by logging into a dapp or anything like that by itself. Unless you are using that exchange with a hive wallet to begin with just like hive-engine's tokens and swap.hive/swap.hbd all work.