Using all of the profane German I had ever heard, I ordered him to come out.
The non-finite clause starts at: "using all of the profane German".
"The main verb has to be: Their main verb is either a to-infinitive , a bare infinitive , an -ed form , or an -ing form :" The main verb for these purposes is defined as the first verb. That is "using" here.
Therefore, the non-finite clause is not "[that] I had ever heard". That is a complementizer clause, which is also subordinate to "using the most profane German":
They are introduced by a complementizer (that, whether, for). They are also referred to as noun clauses, nominal clauses, or completive clauses.
"[that] I have every heard" is a complement of "German". There is an implied "that" for purposes of grammatical analysis.
Types of embedded clauses