They must be registered if you intend on using them in Mn.
ATV Registration
• All-terrain vehicles are classified and registered as either a Class 1 ATV
(under 1200 pounds) or a Class 2 ATV (1200 to 1800 pounds). All ATVs
operated in Minnesota must be registered with the DNR, including those
used exclusively on private property.
Iowa machine will not need a MN temp trail pass unless he used State or Grant-IN-Aid trails.
ATV, OHM, and ORV
A trail pass is required for non-residents operating an ATV, OHM, or ORV that is
not registered in Minnesota on state or grant-in-aid trails.
If he was going to Wis I know he would need a trail pass.
Here are the MN regulations for you to read.
http://files.dnr.state.mn.us/rlp/regulations/ohv/ohv_regs.pdf