Does using a PHP framework (CodeIgniter, Zend) require special server side setup?
I am planning to buy a hosting service and before I do that, I would like to check which frameworks they support. I asked them this and they said they only support Zend.
No php framework I know of needs any special server side setup. PHP frameworks are just that: plain PHP only, as you call it. PHP frameworks are nothing more than already written PHP code for you to build your further code on. Nothing special about it.
People sometimes ask question on 'how to install' this or that framework which derives from the same missconception that frameworks are some kind of bundled software that need complicated distributed installation routines. None of that. Just code you didnt' write yourself. And as that you just need to upload (or download) to server. Done.
I slightly doubt the competence of your hosting company. You might have a missunderstanding with them as 'Zend' often means Zend Optimizer or Zend Guard or such. As to PHP frameworks your host doesn't need to support or not support them. It is entirely up to you what PHP code you upload to that host and who has written that code.
Some hosting companies offer framework support in a way that the frameworks are already available on their servers and are updated by your host. And surely there are a few things that can be optimized like php.ini settings. But in general it will work also without these optimized settings.
I almost never accept hostings that a client has already purchased. When I write an offer I attach the strings that the hosting is chosen by me. If I'm satisfied with what the client already has, the better for him.