Yes, more than one designer can work together.
Can more than one designer working together produce a better design solution than individuals working on their own? Hard to say. It really depends on a number of things.
In my experience, when you get the right group of designers together, things can be much more productive as a group. It requires a certain type of ego for it all to work smoothly, but it can definitely be done.
I've worked in design firms that did the solo model (you 3 designers each go and do your own thing, and then we'll pick one of the 3 to go with) and I've worked in firms that do the group model (everyone come up with ideas, let's get together, brainstorm, iterate, assign tasks, delegate, etc.).
I personally prefer the latter. Being able to think through design problems out loud makes the process much more streamlined, IMHO.