I will say yes....but keep in mind Blue Gouramis can get up to 4 inches if given the room to grow. I bought two and put them in a 20g, and by the time they hit 3 inches I could tell them were out of place. So I transfered them to my 75g and once they fully matured I know they would NOT have been happy left in the 20g.
So might I suggest a dwarf or honey variety of Gouramis for your 20g. If you must go with the Blue...then no more than 2...plus your guppies.
Keep in mind, if left unchecked, you guppies will breed like rabbits...so your 20g tank will in time be filled with them.