You certainly can't check in with your driver's license.
The problem is, according to those rules you'll find in every hotel room in China, if your brother is actually staying in the hotel, then he should be registering at the front desk. For all anyone knows, your brother's visa has expired (or he's wanted by the police, etc.) and you're helping him out by registering for him. They can kick him out after 10pm or so if he's not registered.
As well, if your brother doesn't register, then he doesn't show up in the PSB computer and it's conceivable this might give him problems down the road, especially if he's in Beijing on transit without visa.
Second this. Checking in requires your passport and visa (if your visa is in an old passport you'll need to present them both).
Your brother had better be registered somewhere (or have a good reason he's not--for example, the night we spent on a long distance train.) There have been incidents of people being caught after the fact for not having registered, thus the system is capable of associating the registrations with the visitor. Don't take chances!