Of course it's a language capable of doing so, but as always the answer is, it depends.
I am a Ruby developer, and I love it, and if I was working on an SaaS I would chose it in a heart beat. You will hear people tell you that Ruby is slow, this is true, but I also content that for 99% of cases, this doesn't matter. This really is pointless question though. The question should not be, is Ruby capable of doing this, the question really is, are YOU capable of doing it. If you are capable, then are you stil capable doing it in Ruby? If not, then don't use it. Your customers don't give a ***** what your product is written in, they care about what they see in their browser, and if it helps them, is easy to use etc, am I getting value for money, technology matters little.