Weinstein5 is correct - you can only currently use on vCPU with Fault Tolerance. You are unlikely to be able to size an Exchange 2013 Mailbox server with just one vCPU since I believe the minimum requirement is for at least 2 vCPUs. Of course you can still use vSphere HA to protect Exchange but don't forget that combining vSphere HA with DAGs gives you better availability than would be easily possible with physical servers.
Even if you could make FT work you'd still have a single point of failure in your storage. If you use DAGs then you can keep database copies on different storage platforms to eliminate your backend storage as a single point of failure.
My recommendation is almost always to combine DAGs with vSphere HA for much higher availability. I wouldn't rely on FT to provide you much in terms of availability for Exchange as that really only protects against host hardware failure.
Matt