I believe they are referring to the 6 ft. backyard type antennas,
judging from the linked images on the page. But could the roof mounted
DirectTV and Dish Network type antennas be used for SETI?

Sure, they'd work. The dishes are smaller (1 ft diameter or so) but the
same principles apply as for the larger dishes (8-12 ft).

The only thing is that you'd need to work at much higher frequencies.
You'd need to do SETI at the 12GHz band.
Al


only problem is the signal loss, the 1/(d^2) loss from alien planet to Earth
assuming you keep your antenna directly pointed at his for at least 15
min(rather difficult since neither know where the other is).

If he is 20 light years away, or about 1 E+13 miles away the signal loss is
about -400 dB (at C band)
What this means is that the alien will have to convert a small moon
completely into microwave energy pointed towards earth.
I doubt the aliens could get funding to do it, because they would have to
choose a direction to aim their 1/10 degree beam too.
Listening is the low cost EZ part.
If SETI was really serious they would be building a huge microwave
transmitter.