Some people have reported success without using OIs. However the tactic was developed to use with OIs.Are the OI absolutely vital to success in this tactic?
If you have a coach/***. manager with decent stats in defending and tactics, or you are confident of setting them yourself, then it is probably best to use them. Using a coach/***.manager to set them takes like 2 seconds.
However, each team is different and you may be ok not using them. But, if you don't use them, and your results are poor, then start using them.