Is STCtoCart compatable with WordPress
WordPress is not a shopping cart so STCtoCart will not affect, know or even care if WordPress is installed.
You're asking about two completely different items. What you most likely mean is:
"WordPress can be bridged to several shopping carts. Will this affect STCtoCart?"
The bridge allows them to work together, it doesn't affect the core software. So bridging WordPress with OSC or Zen cart has nothing to do with STCtoCart working as usual with those shopping carts. As long as the shopping cart is working correctly and STCtoCart knows where it is, then it will populate that shopping cart and keep it up to date! The presentation / template etc that the shopping cart shows the products with is completely up to the cart software and has nothing to do with STCtoCart populating the carts database.
Below is a customer that has integrated a Blog with their shopping cart which uses STCtoCart to populate the database!
Example Blog: http://www.mynighttable.com
Example Store: http://mynighttable.com/adultstore/