My humble opinion is that your warranty is clearly at risk if you have a tune. I doubt I could find a tune-friendly dealer simply because I never take my car to a dealer except for warranty work. It is difficult to build a relationship that way. I view a dealer's service department much the same way I would view a proctologist - nice they are available but prefer to avoid them.
If my car was still under warranty and I had a tune, I would see no reason for a dealer to even suspect a tune if I went in for something non-powertrain related - faulty brake caliper, for example. However, if I had my car towed to a dealer with a connecting rod hanging out the bottom of the oil pan or a catastrophic transmission failure, I imagine they might be suspicious enough to do some investigation - and I couldn't really blame them.