Rail bookshelves on a wall with steel studs
There's no such thing as a "standard" screw. Every type of screw has a particular purpose. In this case you do want to screw into the steel studs, and therefore you want a screw with a thread pitch and depth to suit. Most screws provided with shelving systems are better suited to wood studs. 

The first problem that you're likely to encounter is that the "standards" (vertical rails) are usually countersunk to accept a small #6 or #8 flat-head screw, which is a bit on the small side for a massive stack of books. The second is that they system in your photo appears to only be supported every 32 inches. That may not allow enough anchors to be used. 

If you 1) use all available screw holes, 2) install standards on every stud (which means using a shelf system that has brackets every 16 inches), and 3) use the largest sheet metal screw that fits behind the shelving you're using (#8 or #10), I think you'll be successful.