Thank you for your post.
If FileMaker Go on your iPad is connected to your desktop computer running FileMaker Pro 10, then the iPad is a guest of FileMaker Pro 10. Since FileMaker Pro 10 can share the file and allow up to nine guests, you can have up to nine iPads running FileMaker Go accessing the same hosted file on your desktop, eachone modifying data.
iTunes does allow you to install the same application on more than one device. However, if you plan on running FileMaker Go simultaneously on two different devices, then you would need to pay for two licenses.