Having credits isn't the most important thing in the hack itself. However, I would suggest having crediting people somewhere (whether it is in a text file that is with a patch or inside the hack itself in a credits scene so I can appreciate people's help and resources when making a hack).
Well, its important to maintain a credits list for your hack because its giving those what would be otherwise nameless people on the Internet the recognition deserved for the resources they made that you used to make your finished product. Its even of a greater importance if you went out of your way to contact others to make resources and other assets exclusive to your works, that is if they agree to your offer.
A credits list is best kept in a document and I would recommend recording those names down as you obtain the resources you need and/or want.
-------------------- On Pixel Art Requests: I generally do not accept work unless I either have the time, if I see your project worth my time to contribute towards, and that is usually me doing the approaching to you on that.
-I also do not accept speculative work as I do have various art I made on-hand with me.
-I am more receptive to equivalent exchange of resources in which case, you can DM me wherever I have an active presence on for the details.
-Other times I'm availible for your project is C3 request threads I may run.