We had a concrete patio installed late last year on a hot, dry day (in N Wis). We were the last delivery for the concrete truck, and the concrete was poured and finished late in the afternoon. It cured with a very irregular surface with many trowel marks clearly visible, many ridges and low spots in the finished surface. It appears the concrete was too dry and now we are concerned we will have more problems. Does anyone know the likelihood we will have spalling, cracking or other problems given the apparent dryness of the concrete?

By dry I think you mean that the concrete was starting to harden (set up) which would explain the trowel marks etc. as opposed to just not having had enough water added to the mix which is unlikely because they would have just added water for workability.
If it was partially set when they attempted to finish it, I believe you will have problems, especially cracking and if you get serious cracks in your climate, water will get into the cracks, then freeze and expand and widen the crack(s). Or pieces coming off the edges (serious spalling). Without seeing it, it is difficult to say but I think you have at least a 50% chance of serious problems. There are labs that can test the concrete and determine the intregity or lack thereof, and cause.
If the concrete was cured properly such as being kept wet continuously for approx. 7 days, the chance of problems would be less.