I am told Macs (in general) are not very receptive to working with authentication within an Enterprise systems. Is this true?

We recently hired a new Technology administrator who wants to use only PC's at work. His claim is that using Macs are difficult to use in an Enterprise system because they do not integrate very well. Is this true? The organization employes over 1000 people and his claim is that by using a single type of machine (PC), employees will be able to do a lot more (share files, collaborate, etc) with everyone using PCs on the Enterprise system and not Macs. Is this a valid claim? What are the drawbacks with using Macs on an Enterprise system? Any and all information would be appreciated on this topic.