Can I have multiple managers managing a single project?

Yes, it is possible to add a secondary manager who can monitor the project.

To do so, click on a project to open its panel and then click Project Actions ▸ ▸ Access Control. In the new pop-up, click on the user icon for Project Manager and then select the user(s) you wish to add as secondary managers.

These users will be visible on the project's panel page under the Overview tab.