The problem really is the motivation behind imitating can never truly be known unless the photographer adds a written coment. You might copy an image to see how it's done in order to improve your skills. I've tried to imitate pictures to help break out of my own creative 'rut'. I think both of these are fine. It's slightly different when someone imitates another image and then holds it up for scrutiny as their own work because unless the imitated photo is well known, everyone will assume it to be a new concept. Now, I don't know what anyone else thinks about a photo, but for me, the true magic is less in the capture and more in the vision or the idea of a photo - so as long as the photographer is honest by admitting the imitation, then it can be judged on capture alone. As such, I can't understand why someone would wish to publish what should just be an exercize to improve their own work.
There is also the 'accidental' imitation, where the situation lends itself to a well established type of shot. I find this with landscapes, especially if I'm at a waters edge, the sun is rising, and I've got hills in the background. Some of my best shots are the low-angle, long shutter, small aperture type, with a couple of stones just breaking the surface of the smooth reflective water. I haven't set out to imitate anyone else's work, but when I look at it at home and away from the situation, It's nigh on identicle to something I've seen in a magazine - is this a sub-conscious imitation? If you look at the majority of photo's from any given category there's always a trend or fashion, so we're all copying each other to some extent. Thats why I think the intent is important, because how can we judge the merit of a picture if we don't know why it was taken. Unfortunately it's unlikely that someone replicatiing anothers image for their own critical acclaim would ever admit to it!