Go to the Recipe: Shoyu Tare
This is true, but for a tare (and for the ingredient quantities called for), it won't ruin the tare if you use cooking sake. That said, I typically use a dry sake I wouldn't mind drinking, and gekkeikan definitely works, too.
Agreed. I would be very careful in using "cooking sake". It's generally an inferior sake that is then seasoned heavily with salt to stop people from drinking it. As a result you can end up with a heavily over seasoned dish/sauce. I find it much better to use a simple cheap sake that you can usually find in a liquor stores/supermarket, eg Gekkeikan Sake (that is actually brewed under license in California, in the US). Not so good to drink, but great for cooking, and no extra salt!
I could be incorrect but the link for Sake, Dry is a link to cooking Sake.