Remember Miki Moore? He signed after the deadline but was still qualified to play for the Jazz had they made the playoffs. I think the same thing applies to this guy seeing as he hasn't played a regular season game for an NBA team this year. I would appreciate confirmation on this though.
Seems clear enough: "If a player is waived after March 1 (March 23 in 2011-12), he is ineligible to be included in the playoff roster of any team that claims him off waivers or signs him as a free agent."
https://www.cbafaq.com/salarycap.htm