This appears to be a kind of grey area. Microsoft strongly discourages messing with window design elements that are covered by the Themes, since any such customizations would definitely not conform to changes in the Theme designs. Yet the seem to do this themselves in some cases, although those are probably .Net applications. I'll try to do some further research.
A possible compromise would be to create your own standard mini-icon-buttons and insert them the upper right corner of the client area of the dialog. For example, here's how Herman approached it...