The link posted above is the VMware SSL Bible as far as I'm concerned. Read all of it. The shorter answer is no, you can't use the same cert for all of the vCenter services.
However, for View Composer I believe you can use the same certificate you have installed for vCenter if we're talking about a Windows vCenter. The installer gives you the option to select existing certificates instead of using the default self-signed certs, and View Composer is the only View component that doesn't require that you update the Friendly name. I am 90% sure we are using the same cert for vCenter and Composer.
To replace the certificate after you've already installed it you have to use the sviconfig utility. You can find it in the View Composer program directory.
Here's the SSL stuff for View -
Configuring SSL Certificates for View Servers
Update Certificates on a View Connection Server Instance, Security Server or View Composer
**EDIT** - I just checked and confirmed that we are using the same cert for vCenter and Composer. So, there you go. The rest of the View Components do require their own cert, and the links I posted will walk you through that process.