NaHCO3 is a salt of a weak acid, H2CO3, and a strong base,NaOH.

In aqueous solution, the anion undergoes hydrolysis to give free OH- ions and the acid, H2CO3 :

                 HCO3- + H2O = H2CO3 + OH-

Since carbonic acid is a weak acid, it remains undissociated. Hence, the solution becomes basic due to the presence of additional OH- ions produced by hydrolysis. so to answer your question probably your ChIP experiment requires these kind of proprieties of the buffer solution. If you can find other salts that present the same characteristics then sure you can use it instead of NaHCO3.

Thank you