The active ingredient in all vinegar is acetic acid. This will dissolve the calcium compounds that will attach themselves in the hotplate in the steam unit.
However, although acetic acid breaks down into water and carbon products when boiled, it strikes me that if you are implying you will put acid in during steam ironing sessions you will end up squirting dilute acid into your clothes, which may rot the fabric.
Can't see that being a good idea.
For the record, white vinegars are the most pure. Other brown ones have caramel and other natural or inserted flavours in them, that may well gum up the innards of the iron.