There are ways of being an employee that questions and creates change despite being agreeable. But it's about not being an arsehole, being able to meet people in the middle and picking your battles. It's really important to express what you think it's right, whilst finding some sort of middle ground.
If you are completely unagreeable and are unable to demonstrate any empathy for another person's perspective or opinion, you're just simply not going to be a great person to work with at all.
I'm not saying it works everywhere, but you do need to build trusting relationships with people in order to grow within most companies. That trust is built on providing value for being there and also being able to communicate effectively with others even when in a dispute.
Many people I've seen who progress aren't necessarily brown nosing.
Truly a discovery of all time.