Yes, ATVs tires are not DOT rated, so they are not considered legal for road use.   

My concern is related: the ATV tires catastrophically failing at roadway speeds.  Most ATVs are much lighter than a Samurai, so ATV tires installed on a Samurai will likely be at their max load limit.  ATV tires are also much more aggressive than street tires, and I can see all those soft rubber ribs being ripped off at roadway speeds.   It doesn't paint a pretty picture in my mind. 

I run 31" Super Swamper Bias TSLs on one of my beater Samurais, and it is a great offroad tire.  I also flat tow this Samurai to the trails, and they track well on the road too.  The TSL Bias are 6-ply tires, with 4-ply sidewalls so they are overkill for a lightweight Samurai.  However, that means if you run them on the stock narrow rims, you can lower the air to 5psi or even lower.  
I am taking this rig out to a trail clean up run tomorrow.  Love those TSLs!