I don't like dreamveawer and inDesign, they're no more good tools
For html5 validation I use the official validator at w3c:
For epub version 2 I use Sigil and epubcheck
For epub version 3 I use epubcheck
For editing purpose of epub3 I'm usign libreoffice with writer2epub for first part of work (it do a really good job) and then I decompress the epub and work with a text editor (I'm on kubuntu so my editor of preference is Kate).
For epub2 obviously I'm using Sigil.
Just the mobi conversion create some glitch