I know answers here are supposed to be comprehensive but its late, and as no-one else as answered ill give you the short answer.

With contempt. They looked at them as a potential ally but found them disorganised, unprofessional, a liability when it came to keeping their mouths shut and in some areas too far separated from their ideals (especially religion). The Nazi's did try and get the IRA onside at the beginning of the war, but after a while lost interest because of this.