can the speakers be used vertically?

The answer is YES you can mount them vertically right next to your audio/video components BUT you will lose the "whole room filling quality that make these such a great buy. This will occur because these and similar speakers "throw" the sound out in more than one direction and in order to do so the sides need to be unrestricted by any type of solid surface.
You may want to consider using the INCLUDED simple wall mount hardware and get them up on the back wall where they will provide you with the best possible sound experience. if you do this you will be very pleased with the results and the wall mounting is simple, straightforward and requires no real expertise at all. The BEST thing is that if you are having any doubts about where to mount them Bose Customer Service is a simple call or e-mail away and they are easy to deal with and don't make customers wait on hold for an hour and to top it off they are also extremely nice and helpful AND ARE BASED IN THE UNITED STATES OF AMERICA!! in my opinion for this dollar amount you cannot purchase a better pair of speakers for a home theater and music listening system.