Does the jack have a pad on the tube or is it just the round tube? If it is just the round tube then the small footprint of the tube puts a lot of stress on a very small portion of the plastic pads. No problem using leveling pads if it has a foot on the jack tube.
As far as leveling the trailer front to back there is absolutely no concerns about damage. They are engineered with a tongue weight sufficient to support the trailer. Be certain to always use your stabilizer jacks on the front and back so it doesn't tip being a single axle. Too much weight behind the axle can make the front lift off the ground. Always use chocks too.
