Can I sample individual values from an OPC-UA array ?

Yes, if you have an array setup as shown below, then with a sample point as below you can collect the individual data from the array.

{
  "SampleName" : "DistY",
  "SampleDescription" : "Variable VIS_MachineTime.distance[1]",
  "SamplesSaved" : 10,
  "OnlySaveOnChanged" : true,
  "SampleDataType" : "float",
  "OPCUAObject":
   {
    "NodeIdNameSpaceIndex": 6,
    "NodeIdType": "string",
    "NodeIdString": "::AsGlobalPV:VIS_MachineTime.distance[1]",
    "OPCUASampleInterval": 60
   }
},