Can a Brazilian import partner but a partner in a US LLC or S-corp?

Yes.

In general, a foreigner can be a partner in an LLC or in a corporation. However, the corporation will not be treated as an S-corporation for tax purposes if the foreigner is also a nonresident alien. In that case, the corporation will be treated as a C-corporation and taxed as a separate entity. The question, then, is whether the Brazilian partner is a nonresident alien for purposes of American law. A good business and tax lawyer should be able to help you structure this venture and explain the tax consequences of the various options. I hope this is helpful.