Questions about etymology of Ukrainian surnames, toponyms and other proper names are just kind of a questions about etymology.
Still, question examples you provided are not really about etymology of Ukrainian words, per my opinion, rather a "guess a word (name/city) by it's approximate sound"-questions. At least, from our point of view.
If a foreign visitor asks about possible origins of surname
Mdirteko… We'll from his point of view this may look like investigating etymology of the word. But, heck,
Дмитренко is no more Ukrainian word as soon as it was misspelled to "Mdirteko" by some officers. From our point of view it's rather word-guessing, than etymology. (Off-topic: some visitor looked for Sorbonna Square in Lviv; guess what was the actual place name?)
In my opinion: etymology of Ukrainian word is certainly on-topic, but this doesn't apply to misspelled or non-Ukrainian words. I suppose smth like: "We may answer such questions if a word is not so corrupted or just as a gesture of goodwill, but that's not guaranteed: the questions about etymology of non-Ukrainian words or of Ukrainian words that were corrupted in a way that it looks more like 'guess an Ukrainian word by it's approximate sound' than actual investigation of etymology for Ukrainian word, are generally off-topic".
As for separate questions for Петренко, Іваненко, Сидоренко — we'll, if it'll happen, we can write one self-answered question like "How to determine etymology of a surname ending with -енко?" — and mark all these as duplicated — or do I miss something? Still, some of енко-surname questions really worth individual questions (with unclear root).