∃, ∀, ∧, ∨, ¬, are all present in Kobo's built-in Ryumin and Gothic fonts.
However in general I think embedding a subset of a font with all the symbols you need is the right way to go. And for mathematics, rather than just using individual symbols from the embedded font, I would put the whole expression including numerals and variables in the embedded font, because some standard fonts (e.g. Georgia) have lower-case style numerals that look bad in mathematical expressions, or the user might have cranked the font weight up so high that it is hard to distinguish regular from bold variables, etc.
Edit: You might like to look at the STIX fonts:
http://www.ctan.org/pkg/stix for either embedding in epubs or sideloading to your Kobo.