I haven’t contributed a whole lot, but I’d say for my stuff it depends largely on what type of resource it is. Broadly-speaking, if it’s something that depicts a character (portrait, battle animation, map sprites, etc.) that I myself created to represent an OC of mine, assume it is NOT available for use by people other than myself unless otherwise stated. That said…
Item and affinity icons are all F2U and F2E. I feel motivated to make mainly things I have some interest in using, myself, but things like my affinity icons and GBAFE-style icons for non-GBAFE tomes are super general-purpose and I have no problem with anybody using them in whatever hack. The tome icons especially, since those are just edits of existing Dark tomes.
Map sprites (which I have made some of and just not uploaded here yet) are also F2U and F2E unless otherwise stated. GBAFE map sprites are too tiny and simplified to represent any character all that specifically, so I probably wouldn’t mind even if you wanted to use something that was theoretically meant for a singular specific character, since you could just as easily imagine it representing a totally different character whose design simplifies down similarly. Those reordered beta FE6 Mercenary frames don’t even count as my work, since all I did was switch the order of two sprites I didn’t even make.
Maps, I would say are generally not F2U or F2E unless otherwise stated. I’ve been sort of on and off working on ports of maps from some non-GBA Fire Emblem games for fun, and those will likely be F2U/F2E since I didn’t actually design the maps themselves, but fully custom map designs, I’d rather others not use.
Portraits are NOT free to use or edit, at all, unless specifically stated to be by myself personally. Most portraits I make are of my own characters, and I’d really rather others not go yoinking their designs for other things. That said, it also depends on the particular role of the character. If it’s a portrait I made for, like, a throwaway chapter boss or minor NPC or something, feel free to ask and I’ll most likely be okay with it. Recruitable and/or plot-important characters, though? Sorry, but it’s a no-go. Those are just for me.
The opening post kind of implies as much of everything in the repo, but in the interest of completeness, I would not submit something to the repository if it were not F2U and F2E. So, anything in there from me you’re obviously free to go nuts with.
EDIT: I also echo @Sax-Marine’s sentiments regarding battle animations originally made by someone else that I merely made edits to. Credit on something I worked on, even a little bit, is certainly nice, but I’m not too fussed about it until the changes exceed a certain effort level. You are, however, to give credit to the artist(s) who actually did the heavy lifting on the animation no matter what, though, you get me? Any giants upon whose shoulders I stand unarguably deserve the lion’s share of the credit in all circumstances.