I doubt they made the samples in there available for commercial use. I have the EU/UK manual here and had a quick scan through. Despite that though I have not played the game to play with that yet so I am going off what the guide in the manual says.
It mentions a font (Sharp LC or something)
It mentions the conditions for the "challenge" entry and specifically mentions having you clear any third party content sent in.
The music credits part all seem to be classical music and folk songs (presumably all long since out of copyright, though I have not checked all of them and am mostly going by when I know certain composers of the listed tracks died), though performance rights and samples would ultimately mean more there.
As it is not a review, satire, parody or some flavour of education it is unlikely to inherently fall under fair use.
You might have the argument that it is explicitly a music creator but you don't have rights to a sample clip included with one. Equally I might have to pay to use a sound font with a keyboard or something. There were a few examples back when of djs using electroplankton and the korg commercial thing was also popular in certain circles, homebrew again had nice things but those are all different programs. Not sure about Daigasso but that is less relevant than the others mentioned.
A curious one in the end. By strict readings of relevant laws, which is to say samples, I would go with not above board. Practically speaking unless the samples are recognisably theirs and/or you are not sending up one of their songs they might never know, and they would have to be truly petty to go after you. Showing damages based upon that would be even harder (again assuming the rest is not a send up of their song, theme and the game itself is otherwise nothing that would bother them).
If you have the ability to rerecord the song with cleared samples then I would say do so just to be safe. On being sued I would personally be more worried about being sued for my ROM hacks than doing what you describe (with the provisos mentioned) and I am not worried at all about that, I would probably not even be worried about some clever youtube algorithm sample checking and pinging me because I had the title screen with music playing in a video.
Speaking of ROM hacking and before we cover masking techniques if you fancy hacking your own samples into the game then I am down for that, I think a lot of it was covered already but I am still around for it all.