If a non profit board member is also employed at a profit company, when the CEO owns both, is that a conflict of interest ?

Interlocking directorates, even those between a for profit and a non-profit company, do not, without more, give rise to an impermissible conflict. It depends on the whether and to what extent the entities do business and, if so, whether the business relationships are fully disclosed.

Not automatically. It could cause IRS problems if the nonprofit is really a profit company just disguised as a nonprofit. It also depends on the nature of the business and if the employees work for.both.

This practice is neither inappropriate nor uncommon. Conflicts on non-profit boards usually arise not from commercial positions, but from the activities of the non-profit (i.e., self-dealing).