No, up until ArchiCAD 12 (at least), if you don't specifically change the libraries to be loaded, it just keeps them in memory. No re-reading from disk.
Closing a project file by going to File->Close, then re-opening it by File->Open _never_ caused ArchiCAD to re-read anything other than the .pln itself. Not since a long time ago, probably ArchiCAD 9 or 10.
Prior to that it used to re-read the libs even if they were the same.
MacBook Pro 17" 2.4GHz, MacOS X 10.5.6, ArchiCAD 11 & 12, WinXP, Vista (well, not really Vista...)