The only way to be sure the site will work in both environments is to test fully in both environments. Ideally your development environment should mirror your live environment, or you should do proper testing in an environment that does mirror the live. That should give you a reasonable level of certainty.
Joomla itself is very supporting of the various PHP foibles I've seen ... so as long as you meet the requirements for your release, I doubt you'll see any problems with the core code. I can't speak for any you develop yourselves, or any plugins you use however. Best to develop against a mirror of the live version.