"Profit incentive units" is not a recognized term for equity compensation.  You'll need to confirm the structure of this "PIU" to determine how and when it should be reported.  There could also be §409A implications.

If these are really restricted stick units (RSU), §83(b) should not be applicable at all.

Generally, the C&B and Finance teams of the employer would have already taken advice on financial reporting vs corporate tax treatment as well as compensation reporting from tax and accounting processionals when these plans are structured.