I think we may be talking at cross-purposes here. You're quite right that the html character entity commonly known as a tab, if placed in that conf file (either directly or escaped) will render as (and I am prepared to be corrected here) a single space, even if more than one tab were entered.
However, another useful definition of a tab is anything that will render a blank space of a certain width before the next piece of text. And while the code I gave doesn't generate the html tab entities (and couldn't, even if I had placed (escaped) tab characters in that code), the two em-spaces it does generate will create a blank space of a certain width before the following piece of text. In terms of how things will display visually, it does a lot of the job of a tab character.
There are of course other methods I mentioned (css and tables). All three have advantages and disadvantages. It's a trade-off between screen-reader accessibility, coding complexity, and editor complexity. At the end of the day, it's a matter of choosing which one presents the best compromise between these for the needs of your wiki and its user community.