Yep. I just had to replace the amplifier on my Miller & Kreisel Volkswoofer, because my less than intelligent self put a 4 ohm speaker on an 8 ohm circuit. It worked quite well like that for a number of years, until ot didn't.
You can put an 8 ohm load on a 4 ohm circuit and it will work fine. You just don't want to go lower.