I did a pile of research on Yoshitaka Hirota a while ago from the friends section on Mitsuda's web site and Hirota's personal web site with the help of Kago, SquareSound's disappeared translator. Bomberman 64, Bomberman 64: The Second Attack, Faselei, Dive Alert: Becky's Version, Dive Alert: Matt's Version, and Sonic Shuffle all ended up being accredited to his name, when I only thought he did the Shadow Hearts series and SFX originally. SquareSound's
interview with him explicitly mentions Bomberman 64 and he talks about it inspiring Shadow Hearts' music. I think this is the only English confirmation of this, but SquareSound's translator did confirm this.
However, somewhere down the line, it's possible there was a misunderstanding and perhaps he didn't work explcitly as a composer in the actual original Bomberman 64, but perhaps as an engineer or SFX creation. I find it odd that Hirota didn't refute the implication that he did, but, then again, it's equally odd he didn't appear alongside Akifumi Tada on the actual album release. I suspect that Mitsuda's involvement in The Second Attack was down to Hirota and that they co-composed here, and also believe Hirota had a musical role in Bomberman 64 itself, likely a composing one, but perhaps something different.
Don't be baffled that SquareSound is the only place with such info, though, as there was no decent source for Hirota info before that research was done. I'll talk to Zanasea about this and see if he can shed light on the situation. If this doesn't work, I'll try to get some Japanese dude to email Hirota direct, who is usually very happy to receive feedback. I think it is quite likely he'll verify SS' information, but it's possible it's wrong, and indeed it is rather odd.
EDIT: OK, with the help of Zanasea, it's been verified that Hirota did co-composer Bomberman 64: The Second Attack, though there was no specific mention of him working on Bomberman 64 itself on Yasunori Mitsuda's friends page (couldn't read the flash Kanji at Hirota's own web site). So, for now, we'll just say he composed for Bomberman 64: The Second Attack, though it is quite possible that Bomberman 64 also involved him. Thanks for bringing this up; it needed clarifying and has been bothering me for some time.
There's nowhere I can't reach.