For anyone curious as to how a tackled this: I made a Custom Editor View

/App_Plugins/CustomMerchelloPicker/Package.manifest

{
  propertyEditors: [
    {
      alias: "CustomMerchelloPicker",
      name: "CustomMerchelloPicker",
      editor: {
        view: "~/App_Plugins/CustomMerchelloPicker/CustomMerchelloPicker.html"
      }
    }
  ]
  ,
  javascript: [
    '~/App_Plugins/CustomMerchelloPicker/CustomMerchelloPicker.js'
  ]
}

/App_Plugins/CustomMerchelloPicker/CustomMerchelloPickerApiController.cs

using Merchello.Web;
using Merchello.Web.Models.ContentEditing;
using Merchello.Web.Models.VirtualContent;
using System.Collections.Generic;
using System.Linq;
using Umbraco.Web.Mvc;
using Umbraco.Web.WebApi;

namespace CaranteGroep.Catalog.Plender.WebApplication.App_Plugins.CustomMerchelloPicker
{
    [PluginController("CustomMerchelloPicker")]
    public class CustomMerchelloPickerApiController : UmbracoApiController
    {
        public IList<CustomMerchelloPickerProduct> GetAll()
        {
            var merchello = new MerchelloHelper();

            var products = merchello.Query
                .Product
                .Search(1, int.MaxValue)
                .Items
                .Select(i => GetSmallObject(merchello.Query.Product.TypedProductContent(((ProductDisplay)i).Key)))
                .Where(p => (p.Type == "ftProduct"))
                .ToList();

            return products;
        }

        protected CustomMerchelloPickerProduct GetSmallObject(IProductContent product)
        {
            var temp = new CustomMerchelloPickerProduct
            {
                Key = product.Key.ToString(),
                Name = product.Name,
                Type = product.DocumentTypeAlias
            };

            return temp;
        }
    }

    public class CustomMerchelloPickerProduct
    {
        public string Key;
        public string Name;
        public string Type;
    }
}

/App_Plugin/CustomMerchelloPicker/CustomMerchelloPicker.js

angular.element(document).ready(function () {
    angular.module("umbraco").controller("CustomMerchelloPicker",
        function ($scope, $http) {
            $http.get("/umbraco/CustomMerchelloPicker/CustomMerchelloPickerApi/GetAll").then(function (response) {
                console.log(response);
                $scope.products = response.data;
            });
        });
});

/App_Plugin/CustomMerchelloPicker/CustomMerchelloPicker.html

<div ng-app="umbraco" ng-controller="CustomMerchelloPicker">
    <select ng-model="property.value"
            ng-options='product.Key as product.Name for product in products'>
        <option value="">---Please select---</option>
    </select><br>
</div>

On the Peta Poco model

    [UIOMaticField(
        Name = "Product",
        Description = "A product.",
        View = "~/App_Plugins/CustomMerchelloPicker/CustomMerchelloPicker.html")]
    public string Product { get; set; }