I have been using APC for over a year now and without problems on four different servers and more than 30 different sites. All these sites are Smarty ones, using dynamic content literally everywhere. At the moment I am using in a pretty heavily used customer site with no problems. Not once.
APC caches the compiled templates and re-caches them when/if they are altered (compiled by the Smarty compiler). The dynamic content will work exactly as previously, it will only be a bit quicker, of course.
So go ahead and use it.