Simply: yes. Do that. I make custom fabric teaspoons, but I've made some straight away as examples, and also as a starting point to sell them. It's the only way that customers can really see what it is they're buying. Without any photographical evidence, the pillows could be awful, or they might never even exist! Buyers, myself included, want to see actual things, even if it's not the exact one they'd get. A picture of a pillow case is better than no picture at all.
And from what I see the image you have is just of the personalisation? Personally, I'd like to see the pillow case itself being used, ie covering a pillow and sat on a sofa (though that might better suit a secondary pictures), but what's important is that it's evident from the picture what you're selling.
Good luck!
