Hi Liza,
I realise quite some time has passed since your post, but I was browsing through some other posts and found yours without any reply! I recently made a batch of beef sausages, you can find the recipe here
"Beef Sausage" , which have both yellow mustard seeds and mustard powder. I found that the addition of the whole mustard seeds added to the texture and juiciness of the sausage, when cooked they were not hard, but you were aware of their presence in the sausage and they only added a little nuttiness to the flavour rather than any heat. Hope this helps you in some way, I found them to be a very worthwhile addition so much so that I have run out of mustard seeds and will have to order some more from the UK, as they seem to be unavailable here!
Regards,
Richard