A lot of people load that way.
The below info is from American Boating Association.
Boat Trailers How to Choose the One That's Right for You
by Mike Selvon
Boat trailers are as diverse as boats themselves. Just as you researched your boat before you bought it, you need to do the same thing with your trailer. There are a number of styles, shapes and prices, so doing your homework will benefit you. Reading magazines and searching online will give you access to all of the information you need to pick the ideal trailer for your boat.
Boat trailers are sold in two basic types: bunk and roller. Although the bunk trailer is generally considered superior for riveted aluminum boats due to their thin hulls, most boats can be equally supported on either type of trailer. The major difference has to do with how you will load your boat into and out of the water.
Your choice of boating marinas may help you choose between the basic types of boat trailers. A roller trailer is generally preferred if you will mostly load and unload your boat in shallow water. The drive-on, drive-off configuration makes it unnecessary to back very far into the water.
By contrast, the bunk trailer's float-on, float-off configuration makes this type of trailer ideal for those who will mostly load and unload in deeper water. You will need to back the trailer fairly far into the water. Bunk trailers are generally less expensive than roller trailers. Combination bunk-roller trailers can also be found, combining the best of both technologies. These are generally the most expensive boat trailers.
https://www.americanboating.org/equip-trailers.asp