In answer to your queries:

1) No - you don't have to remove your photos from Flickr if Getty selects them....in fact, they put a link alongside your image on Flickr that says "license this image from Getty Images" right on the Flickr site.

2) A couple of my Getty sales were on images that I had previously submitted to a couple of other micro-stock (and macro) agencies and been turned down for "not commercially viable".....so it makes it even better when they sell for much higher prices at the Getty site.