Correct. Two-Way players are not eligible for the playoffs unless signed to a regular roster spot. Their deals can be converted to regular deals up to the last day of the season, I believe.
Ish only has 10 games left on his 2 way contract so they will likely need to make a decision with him prior to the end of the season unless the start DNPing him.
Ideally we sign Stanley Johnson and if Ish outplays either Johnson or Bazley we convert him or have him for as long as we can for insurance purposes incase someone(looking at Warren) goes down with an injury. Anyone we bring on after March 1st wouldn't be playoff eligible so converting Ish would at least give the Suns another body.