Yes they are interchangeable. ‘위해여(서)’is wrong, it should be ‘위하여(서)’ which is grammatically correct. However, you should use ‘위해(서)’ which would be more natural.

나무 뒤에 숨어 있었어요.
[na-mu dwi-e su-meo i-sseo-sseo-yo.]
= I have been hiding behind the tree.

It’s difficult to explain cos it doesn’t literally translate well in English.
숨어 is a noun that means “the act of hiding”. The verb 있었어요 is the past tense of “to exist/to be at a location”.

Since it’s a noun and you are just stating a location with the noun of “hiding”, you don’t use “dwi-eso”.

It’s sort of more like “I am/was at the tree while hiding”. The emphasis in this example sentence is the location that you are at the tree, not necessarily that you’re hiding. That’s how it works in Korean. It’s a noun in Korean. It’s complicated.

If you look at a Korean dictionary, you will find that verbs will end in 다 while words that aren’t verbs will appear as they would normally since they can’t be conjugated.

Think of 숨어 as translating as “stealth” and 있었어요 as “had”.
So 나무 뒤에 숨어 있었어요 would kind of literally translate to I had stealth behind the tree. Having stealth isn’t an action you are doing at the tree, you just happen to be at the tree with stealth. That’s how the Korean language phrases “hiding”.

Proving your fluency is 10 times better than a cert in my eyes

Podemos practicar juntos si quieres, pero yo aún estoy empezando así que espero que no te moleste u.u me puedes agregar si quieres, mi ID es MrSir