PIP doesn't need to be handled it is totally separate from UC.
Providing you are receiving what is now called legacy ESA(CB) then being moved to ESA(IR) will not result in a transfer to UC as legacy ESA covers both ESA(CB) and ESA(IR)
If you are receiving New Style ESA the only way to claim an Income Related benefit is via UC.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems