The usage and its colloquial substitutions are indeed closely comparable, but it seems to me that performing this substitution in German is considered a lot more informal than in Italian.
"Wenn ich einmal reich wär, müßte ich nicht arbeiten" (If I were a rich man, I wouldn't have to work) is unlikely to be substituted by an indicative in normal language. In fact "Wenn ich einmal reich bin" would change the meaning: since we Germans have no dedicated plural forms and eschew using the synthetic forms that we do have, this sounds like a future-tense substitute, i.e. as if I had a firm intention and a full expectation of actully being rich at some well-defined point in the future.
The only situation where I recall ever hearing the substitution except literally on the streets is during sports reporting. "Oh nein! Wenn er da nicht ausrutscht..." (Oh no, if he hadn't slipped [...he might have scored]) can occasionally be heard, but only when the reporter is too excited to correct himself.