This is hard to answer cause people who went the trouble archiving other dev's games must have a reason. Though not necessarily good reason.
If you're only discussing this matter in the forum like this, IMO it's fine. However, if you're going to make video about this, I highly recommend you to ask the games developer's comment and those people uploading those games first! listen from both sides so viewers could get enough insight and make their own judgements.
How do you feel about people archiving indie games? How would you react if you found a re-upload of your project?
I give them my positive thought about them that they are doing it for good cause. But only if they specify the name of the developer of the games they've archived.
If they uploaded my games without asking me, I'd ask them why.
What if the game in question was removed by the creator? Does this change your answer to the previous question?
No. I'd still ask them why.
In your opinion, is there any situation in which it is morally acceptable to re-upload a game you do not own?
Only if it's done for preservation purposes.
What preventative measures can developers take to prevent their games from being re-uploaded by a third party?
Probably nothing. If you've shared your games to others, they have copy of your games and they could anything with them including uploading. If you don't want people to reupload your games then don't share them in the first place.