The galaxy is so vast, never the twain shall meet.
They found the federation didnt they?
And all those saying they would just assimilate the Vorta and Jemhadar. Do you really thing they would let them?
Both would kill themselfs or each other without hesitation.
They would destroy a whole world just to prevent falling into borg hands.
In a Borg Dominion war I could see whole species caught in between wipped out.