Does the OpenZeppelin project offer security audit services for other projects and companies?
No, OpenZeppelin doesn't make security audits. OpenZeppelin is a community project that builds a framework of reusable smart contracts. The project doesn't offer any auditing services for things not related to the development this framework.
The confusion arises because OpenZeppelin was started by the Zeppelin company. Zeppelin is the main supporter of the project and most of the OpenZeppelin maintainers are also Zeppelin employees. Zeppelin offers audit services, but as a complete separate branch from the work they do to support the OpenZeppelin framework.
OpenZeppelin has contributions from many different companies and individuals, some of which also provide auditing services. The OpenZeppelin slack has a #jobs channel where people can get in contact with members of this community that provide these auditing services.