I think that is probably correct, however I have never heard anyone say "de wa arimasu" before. Usually, the long form is only given when it is negative; "de wa arimasen." From that, I can logically see how you would think of "de wa arimasu." If you want to ask a Japanese person about this, here is how I would ask:
"(nihongo de) desu to iu no wa, de wa arimasu no shouryaku desu ka?"
(日本語で)「です」というのは、「ではあります」の省略ですか?
"Is 'desu' an abbreviation for 'de wa arimasu?'"
I put "nihongo de" in parentheses, because, contextually, it isn't necessary to say that.