No, there is no requirement to call level in radar environment. Personally, I find it a mite irritating, as some pilots use it to infer a request for a higher level, particularly when using the phraseology "reaching FL...."
I would add, however, on the common sense front, that if you, as a pilot, were instructed to reach that level with a restriction (r.o.c, time etc) then it is often due traffic. In this case it may be useful to the controller to know the level has been reached, thus the conflict is solved.
I am sure there has been nothing official in this area since the introduction of RVSM, but I'm prepared to be corrected in this matter.