Which macs are compatible with OS X 10.11 El Capitan?
If you care to read the tea leaves, the initial OS X v10.11 Developer Beta supports the following Macs:


iMac (Mid 2007 or newer)
MacBook Air (Late 2008 or newer)
MacBook (Late 2008 Aluminum, or Early 2009 or newer)
Mac mini (Early 2009 or newer)
MacBook Pro (Mid/Late 2007 or newer)
Mac Pro (Early 2008 or newer)
Xserve (Early 2009)


Source: OS X v10.11 Developer Beta 1 Release Notes. 

No official requirements are published by Apple. 

About your last question, no. There are no macs supported by Yosemite that are not supported by El Capitan.