There are always three generic fonts available to an ePub, serif, sans-serif and monospace. They can in principle all be the same, but Adobe does provide separate serif and sans-serif fonts. The default font is serif, and you will get this unless the CSS is exactly right to get an alternative. As you suggest, this requires more than having the font on the machine.
Last time I checked, it was possible to edit the CSS of an ePub to address a font with the Windows Sony Reader, but not with Desktop ADE. See
User Stylesheet for Adobe Digital Editions. The same approach works on many, but not all, dedicated e-book readers using mobile ADE. However, they all have different locations for user provided fonts - so the ePub's CSS must be customized for each device.