Pragma syntax is unique to squeak, I believe. This is included in 3.9 and later images
No. Squeak Pragma are compatible to the ones in VisualWorks, GemStone and GNU Smalltalk.
I've compiled a list of syntactic/library differences (that matter to Seaside) in my this years ESUG presentation:
http://www.lukas-renggli.ch/blog/seaside-presentation-esug2008
Lukas