OpenICF framework used to be compatible with ConnId. But it is no longer compatible. Therefore stock OpenICF connectors cannot be used in midPoint. Older or modified OpenICF connectors may still be able to work with midPoint. However, their use is not longer supported.
OpenICF is a descendant of Sun Identity Connector Framework (Sun ICF) which was probably the only usable open-source part of Sun Identity Manager. OpenICF is now an open project governed by ForgeRock. Although there was a significant number of improvements over the original Sun version the basic approach and architecture remains the same.
OpenICF used to be compatible with ConnId framework, it is sharing the same architecture, concepts and significant part of the code base. But there are some unilateral code changes made by ForgeRock that made the connectors incompatible. Please refer to the ConnId and Identity Connectors pages for more details.