I was once with a group at a small local observatory, trying to take a look at Venus, low over the horizon. As the rotating roof rolled into the correct position, it turned out that a Yagi-style antenna mounted outside sat right in middle of the view. It seemed like something that'd ruin your day (or night), but it turned out that it really made no noticeable difference.
Yes. Given enough distance, the obstructing object will start to come into focus, but if it's close, it just darkens the image. After all reflecting telescopes have a secondary mirror (along with its mount) permanently obstructing part of the primary mirror.
