By default, no. In order to legally embed fonts into ebooks, you have to have a license to do it, and most people don’t have one.
When you buy a commercial font, in most cases you buy a desktop license, or desktop + web license package. Ebook embedding license is a separate thing that costs extra. Sometimes that cost is quite high, which makes people decide against it.
However, if you have a license to use a commercial or free font in ebooks, then embedding is more than welcome.