There are 2122 possible v4 (variant 1) UUIDs (from Wikipedia). It doesn't really matter what representation of them you use - there are still the same number of values, and you can presumably assume that the attacker knows the format being hashed and can transform or add dashes as required.
Given that 12 completely random characters used as a password are infeasible to crack, and that is merely 9612 (assuming 96 potential characters, based on a standard keyboard), you get a good indication of why the UUID is unlikely to be guessed.
The 12 random character password has 612709757329767000000000 (ish) potential values. The UUID has 5316911983139660000000000000000000000 (ish) potential values (all values from Excel, which is not designed for such large values!). For reference, the 66 in the UUID count corresponds to the 61 in the password count.