As a Hoster, I also find it very odd that any Hoster would not have Zend Optimizer installed. Can't see running a Server without it actually.

Usually, when viewing the Server/Version Info page you will see this near the top, last row in the TABLE:

Registered Stream Filters

Just underneath that is the Zend information, along the lines of:

This program makes use of the Zend Scripting Language Engine:
Zend Engine v2.1.0, Copyright (c) 1998-2006 Zend Technologies
with Zend Extension Manager v1.2.0, Copyright (c) 2003-2006, by Zend Technologies
with Zend Optimizer v3.2.2, Copyright (c) 1998-2006, by Zend Technologies