First of all, Dexter's web site recommends a few brands of grease and Pennzoil 707L is on that list and Lippert's recommended list also. It's red and has a high drop point (holds up to heat). Also some web sites do not recommend combining two different greases. They recommend washing all the old grease out and then hand packing.
There are a substantial number of articles and forums you can read on the Easy Lube Hubs. I personally think they are great for a boat trailer but the possibility of putting too much grease in the bearing cavity is very great! My previous 5th wheel was pre owned when I got it and the brakes simply did not even begin to work. Pulling the manual lever on the brake controller did nothing. I took the brake drums off and what I saw was unbelievable. The brake shoes and magnets were totally covered in grease!!!!!!!! I called the previous owner and ask him about it. He said "why sure, we always put grease in the zerk each time we prepared for a trip." I did not replace the brakes but washed everything down in gasoline and lacquer thinner. I replaced the seals and hand packed the bearings. Brakes worked great after that.......for a while. Then I noticed little braking ability when using the manual lever. I removed all four wheels again and apparently grease had oozed out of the brake linings and contaminated the drum surface. So I cleaned them all our again. Brakes good for about a year then same thing....more grease had oozed out of the linings. I put up with this for a few years, never replacing the brake shoes and finally when I traded it in last year for a new 5th wheel with new brakes I was totally shocked at the braking power I had. Never had I been able to stop like this!!!
Bottom line....don't use the easy lube zerk fitting. Hand pack your bearings and use quality grease at least every other year depending on how many miles you travel. If your shoes are already contaminated then REPLACE THEM now.