Ok I verified it with positive results, I think it's the burner, HL-DT-ST DVDRW GS23N SB00 (ATA) that for some reason makes unreadable copies for the Wii. Still, when I finally did some research and figured out it was an LG-Hitachi model, I still can't booktype DVD+R to DVD-R, it says after Current Setting: Unknown (FAILED!)
Reason: Invalid Command Operation Code
Perhaps the IMGBurn version 2.5 does not support this driver currently? The MacBook Pro is like 2 weeks old.
In the meantime I'll try to get ahold of some friends who have different externals to use.