There are lots of pros and cons about the ramp. You are overloading the good tire by putting the entire weight of the side of the trailer on the one tire. Is this enough to hurt the tire???? Who knows, but it could damage the cords in the good tire enough to cause a problem later. I don't think any of the tire manufactures will recommend the ramp.
Also,, you should never jack on the axle tube itself. If the axle is under the spring, you should jack on the frame, if axle is on top of spring you can jack on spring. If you jack on axle and cause a dent or collapse the spring in any way, you could change the camber of the tire which could cause excessive tire wear, or even cause axle to become loose in u-bolts.
Just my 3 cents worth.
Jim M