Hopefully I can provide some sort of assistance.
* Donkey Konga USA/EUR/AUS
-Have access to it, but the copy has gotten a bit beaten up and won't always run properly. I do not recall at any time seeing any sort of credits roll. The manual is also lost, so I am unable to look into that.
* Dr. Mario Online Rx USA
-I have done research into this myself as well as asked the people I know who play this copy the most. None of them have claimed to see any sort of credits roll at any point in time. I looked into the Online Instruction manual for information and found nothing. I would personally conclude this as No Credits Exist.
* Yoshi GB/NES
-I have a copy of the GB version and I do not recall during my years of play ever coming across one. I also am unable to locate the manual for the game. Based on the other old School GB titles I read instructions for, I do no believe the manual would contain the credits. I will try work on this when I can to see if a particular score must be achieved for the credits to roll. However at this time I'd state No Credits Exist.
* WarioWare DIY
-A friend has a copy and claims that a credits roll is available for viewing at any time. I'll try to get a video recording of the credits ASAP, probably within a couple days.
The following I have access to but have not researched the matter yet:
* Super Smash Bros. Brawl
* WarioWare DIY Showcase
* WarioWare: Snapped!