Got asked about webcenter accessability today, and the answer is obsolutely yes
Oracle WebCenter 11gR1 has been tested against Oracle's Accessibility Guidelines (OGHAG), that combine guidelines of Section 508 and WCAG 1.0 'AA'. Here are the links to the product VPATs:
VPAT for WebCenter Framework 11gR1: http://www.oracle.com/accessibility/templates/t1008.html
VPAT for WebCenter Spaces 11gR1: http://www.oracle.com/accessibility/templates/t1684.html
WebCenter 11gR1 PS1 has been tested against the current iteration of OGHAG, that factors in WCAG 2.0.