In general, the placement of "всё" does not matter.
Собаки всё ЕДЯТ
Собаки едят ВСЁ
ВСЁ едят собаки
All the three versions are correct and have same meaning. Well,there can be a nuances.
For example, the first sentence sounds a bit like you say it with annoyance, just like "Oh, dogs eat everything! They chew my chair, my shoes, and my rubber plant!" The second one sounds more encyclopedic, like "Meat, cereal, vegetables, etc. Dogs eat everything (from this list)". And the third sounds like you are pointing to the box with meat, cereal, vegetables, etc and explaining to your guest: "That's the food for my dogs. Dogs eat everything (from this box)".
But! The intonation is the queen of Russian language. You can use any of the three phrases in any meaning, just do a stress on the most important part of the sentece. Russian has a tendency to put the logical=intonational stress to the end of the sentence, and sometimes in the very beginning (I marked the intonational stress by CAPS LOCK).
Ты хочешь ЧАЙ? — Do you want TEA (exactly tea, or, may be, coffeу or juice)?
Ты чай ХОЧЕШЬ? — Dou you WANT tea (or you don't)?
ТЫ чай хочешь? — Do YOU want tea (or your friend wants)?
A lot of the flexible word ordering is because most nouns decline in Russian. So I can see that if at least one of the nouns - subject or object - can decline, all is well. But many nouns of foreign origin often don't decline. So what flexibility would there be in ordering in a sentence using 'есть' (to eat) in the case of two nouns, neither of which decline? Would you have to stick with Subject Verb Object? Or could you use Subject Object Verb? Would there be any cases where the Object could come first if neither subject nor object are declinable?
This is indeed common for printed text. I have wondered this myself, but reality there is actually very rarely any ambiguity because of context and syntax. For example "Все собаки едят все" is only valid if the first "все" is interpreted as such (at least without extra punctuation) and the last one can only be "всё", because "всё собаки" would mean something like "the dog''s everything" (singular) and if you wanted to say that they're eating everyone, you'd say "все собаки едят всех". It gets to the point where you don't even notice whether the text prints the dots or not, but are able to read it correctly without thinking.
Всё means both, no matter what. That means you can easily use it wether it means "anything" or "everything" in English.
However, when you translate to English, you need to know when to use "anything" or "everything"... in English, not Russian. Here, you need to check an English grammar book/dictionnary, not a Russian one.
In this case, because the context is wide, you can use both "anything" and "everything". If your answer "Dogs eat everything" wasn't accepted, report it. It should be.
But since 'ё' is usually written as 'е', "Все собаки едят" could instead really be "Всё собаки едят," which would mean "Everything here is eaten by dogs" and not "All dogs are eating," right? How do ambiguities such as this get dealt with in Russian? I imagine if it occurred to someone that this might be ambiguous, they might put the dots on the 'ё', but often, I guess the creator of the sentence might not notice the other way the sentence could be read.