Regarding Deut 29:28 (ET 29:29), Jason Staples writes that this “is the only place in the LXX that κρυπτὸς and φανερός appear together” (Paul and the Resurrection of Israel, p. 169n90). He sees a strong allusion to this verse in Romans 2:28-29. Depending on what counts as LXX/OT, this morning I stumbled upon another pairing, in 2 Macc 12:41:

πάντες οὖν εὐλογήσαντες τὰ τοῦ δικαιοκρίτου κυρίου τὰ κεκρυμμένα φανερὰ ποιοῦντος

Staples' claim may be stricter than mine, referring solely to the adjectival and not other forms, but given the context of the passage—idolatry, sacrifice, resurrection, and divine judgment (not to mention praying for the dead!)—I thought it notable as another echo for Saint Paul’s use of the terms.