Hi,
Yep SEBLOD 3 works with PHP 5.2, 5.3, 5.4
Everything has been done in order to be compatible with all, but we don't have any website/customer on PHP 5.2 anymore.. so we don't really test it on PHP 5.2 these days... If you see something wrong, feel free to report on the tracker, and I'll have a look.
Regards,
Saba.