If they came with a Steam key, yes you can put them in your Steam game library.
To see if they have Steam keys, go to the Humble Bundle page and login. Click 'My Account' in the top right, you'll see a list of all games you've purchased. Scroll down and you'll see a list of Bundles you purchased. Click on a Bundle you purchased and a new page will open, on this page any games that have Steam keys will be listed at the top, you just have to click the Steam icon to view the Steam key.
To add games to your Steam library, start Steam and login. Go to the Games menu and select 'Activate a Product on Steam...' This will open a new dialog box, click Next then I Agree for the Subscriber Agreement. The next screen has a place to enter the key from your Bundle purchase. I don't have one to test and I don't remember exactly, but there's something like a choice of adding it to your library or downloading immediately. Either way, you'll see the new game listed in your Steam library.
