If someone has been denied a tourist visa to the United States 10 years ago as a Brazilian passport holder, would they be ineligible for a J-1 visa as a German passport holder?
A past refusal does not create automatic ineligibility for a future visa, but the reason for the prior refusal is significant. If the prior application was refused because of some ground of inadmissibility that still pertains to the applicant and is also relevant to the future visa, then the future visa should also be refused.
These are completely independent applications. The result of one does not bare onto the other.
Whatever reason for refusal may apply to the new application though, if it has not changed since then.