Yes, I have seen "diagnosticians"......but only with fairies, unicorns, and lepricons!
Sorry, had to say that. I know, I am bad.
On a serious note, no...there are no doctors like "House MD" in the real world. Medicine is very specialized..even sub-specialized. All MDs are diagnosticians in their own speciality.
The closest thing to what you describe is probably Family Medicine (maybe even Internal Medicine, and Emergency Medicine). But then again, you rarely see "zebras", mostly "horses".
Pathologists are the "doctor's doctor", and all they do is diagnose all day, but again...they are not clinicians, they usually do not see and treat live patients. They diagnose disease by looking at, and analysing, tissue samples in the lab or morgue.
In real world medicine, all MDs see and treat common conditions....Thank God for that. If this was not the case, the job of the MD as a healer will be much more difficult, and frustrating.
Good Luck!