What's a typical percentage of income tax for an employee owned company?

This will depend on the entity type of the EO company post-transition, how the functional corporate federal and state income tax is impacted.

A 100% S Corp ESOP, for example, is 100% corporate income tax exempt, however this is more of the exception among EO corporate forms than the rule.

In worker co-ops, there is typically an income tax deduction that can be taken on whatever portion of profits will be pro rata allocated to worker owner individual capital accounts (as opposed to profits which would arise from non-employee-owner employees, which are taxable to the co-op).