Ben is correct. Any prospecting vehicle can find Alazhi, but the chances are far less because that same prospecting vehicle has a proportionate chance of finding any other deposit type that same terrain can support. The alazhixazha can ONLY find alazhi - that is, if it finds a deposit, it will 100% of the time be alazhi.
Groundhogs have 480 sensors in a squad. alazhixazha have 120, and FKs have 120. Of course Groundhogs have the greatest chance of finding a deposit on any given square, but alazhixazha and FKs have the same chance of finding a deposit.
So, looking at say a forest square using both FKs and alazhixazha. Both squads have the same chance of finding SOMETHING. alazhixazha can only find 1 deposit type - alazhi. If the FKs find a deposit, it could be Ardanium, Duracrete, Alazhi, Nova, Varium, Durelium, Lowickan, Vertex or Berubian. So, if the FK did find a deposit, there is a 7.255% chance it will be Alazhi; if the alazhixazha found a deposit, there is a 100% chance it will be Alazhi. For argument's sake, let's say there is a 10% chance you find a deposit using 120 sensors. That means, on any given unprospected forest square, there is a 10% chance you find Alazhi using alazhixazha, and a 0.7255% chance you find Alazhi using FKs.
This explains why it is so comparatively rare to find Alazhi using FKs/Groundhogs, and why those looking specifically for Alazhi on their terrain should use alazhixazha.