First of all two eNodeBs operating on same frequency would create interference to each other even though PCI get selected using Zadoff-Chu and M-Sequences where these sequences should have good correlation properties. In field deployment, each operator uses different frequencies. It is possible multiple operators are part of same band but they would operate in the different frequency range.
For example : In LTE band 40 (2300 MHz to 2400 MHz) TDD band, multiple operators such as Airtel and Aircel work.
The objective of proper PCI selection is to reduce the interference between two neighboring cells which are operating in same frequency.