template.array.merge.json

{
  "$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "arrayA" :{
      "type": "array",
      "defaultValue": []
    },
    "arrayB" :{
      "type": "array",
      "defaultValue": []
    }
  },
  "variables": {
  },
  "resources": [
  ],
  "outputs": {
    "Result": {
      "type": "array",
      "value": "[concat(parameters('arrayA'), parameters('arrayB'))]"
    }
  }
}