You're going to get answers from both sides of the pack, but you should understand that there is very little that the competitive Smash community considers "cheap." "Play to win" is a credo here, and the competitive community tends to feel that you can and should use every option at your disposal to win. This isn't really as "dirty" as it sounds. It just means that we like to recognize, understand, and be capable of utilizing every option available to us.
Smash is about more than colossal hits that can't be recovered from. There's as much depth in the strategies and counterstrategies involved with keeping a player off the ledge once he's there as there is in any other aspect of the game.
There is, however, a portion of the casual community that feels such tactics are "cheap," though people "graduate" from the mindset relatively often, as they become involved with the game and get better. Few, if any players, do the opposite--go from believing it's okay to believing it's cheap. Those who do regard it as cheap are usually met with strong opposition, even from within the casual community.
My attitude, and the attitudes of many many players, is that there's no reason to limit your own capabilities. If you can fight to keep a person off the edge, in addition to fighting to get them there, you should do so.