Hi
It should work.
As per vCenter 5.5 Deployment guide, "The recommended approach for deploying vCenter Server in almost all scenarios involves a single virtual machine for the vCenter Server components and a separate virtual machine for the vCenter Server database."
The recommendation (soft recommendation) to centralize SSO+Web Client is when you have more than 8 vCenter servers.
When to Centralize vCenter Single Sign-On Server 5.5 | VMware vSphere Blog - VMware Blogs
"There can be increased risk when centralizing a vCenter Single Sign-On server (to why it is not recommended for smaller environments) due to the increased number of components affected if the vCenter Single-Sign-On server was to become unavailable, in short all vCenter Server components of all vCenter Servers registered will incur authentication loss (when compared to just the single vCenter Server instance when installed locally) and so availability of the vCenter Single Sign-On centralized server(s) is highly recommended."
With single VM hosting SSO+WebClient+Inventory Service+vCenter Server. It would be easier for you to manage, backup, etc.
Do you have HA license in your vSphere environment?
HA should help you to restart SSO VM when the SSO VM dies.