there is no silver bullet, html5 or not at the end of the day a no mater what you use the video can be ripped.
There is no security protection of any sort in the world that is 100% bullet proof, any security can be breached, this doesn't mean you should just abandon any effort to make things secure. I was working on a coding project once and one of the other developers made a plugin for the main system that was storing the user passwords as plain text in a cookie, on top of that it was disabling the ssl connection, when I called him to talk about that he was like "If a really good hacker wants to hack into user accounts he can do that anyway, it makes no difference"; I couldn't believe that was happening.
As someone else mentioned in another thread, people tend to think they have more rights over the content when they can download it, when it's protected even if they jump hoops to get it they are very aware that it's obtained illegally, it makes a big difference
So as a conclusion:
can you protect html5 video - YES
is it bulletproof - NO (nor is anything else)