Question: Is it possible to limit access to a page using wordpress user roles that isn't included in the wordpress install.

For example I have a CS Cart install with only a couple of products but I need to limit access to these pages to certain users.

Can I add something in to my CS Cart install to call on Wordpress to be able to limit access if the user is just a subscriber?

Answer: 
if you can include the `wp-load.php` from WP install; after this you can use all WP Core functions and can also check the user and his rights with core function - `current_user_can()`.

But maybe it's easier to create an bridge from CS Cart to WP, if CS Cart has an own user table; i dont know.
No, it is not possible, not cleanly anyway

There are kludges that will get you half there but they are ugly, and trivial to bypass, making it a waste of time, and time is money. It would thus be insecure, costly to build, and costly to maintain, without actually delivering the goal.

You would be far better off going with a piece of software that integrates directly into WordPress, such as an eCommerce plugin, most of which are free and have a lot of features, e.g.:

* Jigoshop
* WooCommerce
* WP-Ecommerce