Yes and no. You would need to installation for each corresponding version but you can have them all installed on one computer. I publish the vSphere Console via Citrix and have it working for 5 and 5.1 without incident.
1. You can just run the 5.1 installer over the top of an existing 5 installation and it will work for both versions.
2. You can install 5.1 and then try to access a 5 farm and the bits will be added to the existing version.
Technically, what the gentleman said above is accurate but I believe you were asking whether a single system with the vSphere client could access multiple versions which is indeed the case.
