Are for-profit companies possible in Ethereum?
You can definitely write a smart contract with a designated address as the "owner" (usually implemented as owner = msg.sender in the constructor). The contract can then implement certain privileges for the owner, e.g., the right to take a 10% fee off of every transaction in the contract. The benefit compared to the centralized company is twofold:


Users interacting with the contract can see the rules in advance and are sure that they won't change (i.e., decentralized Uber, if correctly implemented, can not opportunistically refuse to pay a driver);
A third party, such as law enforcement, can not shut the whole enterprise down.


The question whether DAOs are fully compatible with standard firms requires the definition of compatible. I suppose it depends on the jurisdiction.