According to the Adobe release notes ADE 4.0.3 for Windows supports MathML. However, I have been testing epub readers and so far I have found only Apple iBooks epub reader, Readium app for Chrome epub3 reader, and Calibre displays MathML correctly. I have also tried to display my MathML test equations in FireFox, IE, Chrome, and Safari browsers and found that only Firefox (38.0.1) displays the MathML equations correctly. The other three browser do not display MathML.
Here is my test epub that I have been using to test ePub readers. It containing two MathML equations, area of a circle and the quadratic formula:
https://dl.dropboxusercontent.com/u/...tester-v2.epub
Hope this helps.