Everyone is right that it is possible. That being said, the official recommendation is to deploy a seperate instance with Azure AD Connect. The features that get rolled into and released to Azure AD Connect often are unavailable using the Azure AD MA with MIM.
Yes highly recommended to run Azure AD Connect as your identity bridge between on premises and cloud as it is frequently updated in sync with updates in Azure AD as well as in Office 365 in hybrid mode. In a FIM/MIM instance these frequent updates on the connector could make updates/changes that affect other connectors and more often than not organizations really dont want to touch their configured connectors and sync schedules.
So yes the best practice is to have Azure AD Connect be your connection between AD and Azure AD.