Yes, Seattle's buses have them but don't expect the drivers to help you out if you've never used one. I tried to put my road bike on one last week, not having used one before and was really struggling. It took me a good 2 minutes of trying without success, and the driver finally honked at me and yelled that she had to go, which left me with very nasty thoughts in my head and no bike on the bus.

Fortunately, the metro website has a video showing how to load your bike onto the rack, and I watched it while waiting for another bus to show up, having success the second time.