Hi Miguel,
I guess for SL distribution, it should be based on GPLv2, but if you are 
asking license for each package, I believe some of packages would not be 
GPL, such as "bind" which would be BSD license I guess. Whatever, most 
of packages should be GPL with any version, you can check them by rpm 
-qi <package name>.

Or you can check either your SL iso(if you have downloaded it) or online 
repositories:
http://ftp.scientificlinux.org/linux/scientific/6x/x86_64/os/
http://ftp.scientificlinux.org/linux/scientific/5x/x86_64/

And search any directory about "repoview", you will see a lot .html for 
specific package in there, for example:
http://ftp.scientificlinux.org/linux/scientific/5x/x86_64/SL/repoview/authconfig-gtk.html
http://ftp.scientificlinux.org/linux/scientific/5x/x86_64/SL/repoview/tunctl.html
http://ftp.scientificlinux.org/linux/scientific/5x/x86_64/SL/repoview/automake16.html

Just open the html, it will show you what GPL version it is then.
Not sure if that answer your question?


Felix Lee ~
-- 
Felix Lee                               Academia Sinica Grid & Cloud.
Tel: +886-2-27898308
Office: Room P111, Institute of Physics, 128 Academia Road, Section 2, 
Nankang, Taipei 115, Taiwan