In the Stardust Crusaders series, the antagonist Vanilla Ice is localized into English as "Cool Ice". There's also the renaming of Steely Dan to "Dan of Steel". Is it due to possible copyright/trademark infringements? Or is there another reason, artistic license?
I found a page from the US Government's Patent and Trademark Office that explains when a musician can trademark a name. http://www.uspto.gov/learning-and-resources/ip-policy/musicians-and-artists-profile, under Registering a Name:
Sometimes musicians and artists want to register their name as a trademark, including a stage name or pseudonym. If the mark appears to be a person’s name, then there are additional requirements for the application. If the name is an actual name (including a nickname or stage name) of any living individual, then the person’s consent to the use and registration of the name must be included in the application file. See TMEP 813 & 1206.03. If the mark does not refer to a living individual, but could be interpreted as a name (e.g., a band name that looks like a person’s name), then a statement that the mark is not a living individual must be in the application file. See TMEP 813.01(b). In addition to the consent requirement, applications seeking to register a performer’s name as a trademark must include evidence that the mark appears on at least two different works (e.g., multiple CD covers). See TMEP 1202.09(a). Applications seeking to register a name as a service mark must show a use in connection with the service, and not merely the artist’s name or the name of the group. See TMEP 1301.02(b). However, an artist’s name or pseudonym affixed to an original work of art (sculptures, paintings, jewelry), need not show use in connection with a series. See TMEP 1202.09(b).
I couldn't find any specific source saying that Vanilla Ice and Steely Dan were trademarked, but it seems likely they are. (So we should really write Vanilla Ice™ and Steely Dan™.) The names have appeared on several CD covers, so that clause is covered; and it seems unlikely that the actual name of any living person is "Vanilla Ice" or "Steely Dan". (But even if there was a "Vanilla Thaddeus Ice" living in Gary, Indiana, the kind of money that a major record label used to be able to command could probably convince him to give permission for the trademark.)
The US fair use laws do list parodies as a protected class of work, so according to what little I know of Jojo's Bizarre Adventure and fair use law, it could probably be argued in court that this is a parody and therefore a protected usage. But I imagine the translators wanted to avoid any risk of going to court to argue about this, so they voluntarily changed the names.
I don't think are there any real copyright or trademark issues that would prevent the names Vanilla Ice or Steely Dan being used in the English localization. You can't copyright a name and I don't think trademark law would apply because there's no chance a consumer would confuse these very different products. In the case of Vanilla Ice his abandoned registered trademark in the US would have only covered "Audio and video recordings featuring music and artistic performances [...] T-shirts [...] Entertainment in the nature of live MUSICAL performances by AN INDIVIDUAL [...]", and not characters in comic books and cartoons. On the other hand, Steely Dan's name is not exactly original, they took their name from a strap-on dildo in a William S. Burroughs novel. Also copyright protection is automatically world wide, and trademark protection goes wherever the product does. I don't know if Vanilla Ice ever had much of presence in Japan, but Steely Dan has toured there, so the group would be entitled to just as much protection of their name in Japan as the US.
That said, even if they don't have a leg to stand on, it's much easier for an American to cause legal trouble for an American company in the American courts, than it is for them to do the same to an Japanese company in a Japanese court. The company doing the localization might have very well changed the name to avoid a legal fight they couldn't afford even if they were certain to prevail in the end.
At least for the Vanilla Ice character there's another fairly obvious reason why the name would be been changed. Many Americans would recognize the name and be put off by the fact that the character doesn't actually resemble the rap performer. Even without the legal considerations they may have changed the names of the characters (there are quite few using names of musicians) to avoid all the baggage the names would have with American audiences.