EAGLES recommends specification of diathesis alternation and argument optionality in the lexicon, although this is not a universally adopted practice, as witnessed by those lexicons which list alternating frames as completely separate and unrelated lexical entries (e.g. Eurotra).
In EAGLES, diathesis alternation phenomena are captured at the frame_list level, which can be interpreted as a paradigmatic structure, where all alternants are encoded on a par. The main advantage of this encoding scheme is that all possible alternations are entered in the lexicon on a par, meaning that no single alternant is given a privileged status, say as a base from which all other alternants are derived through some lexical rule.
As for argument optionality, two alternative ways of encoding it are made available: either as a particular case of frame alternation (which requires listing of two distinct frames), or as a single frame where the optional argument is marked for optionality through feature specification.