Uberti offers the 1873 in many modern calibers. Like .357 Magnum and .44 Magnum.

is t safe to shoot these rifles using smokeless loads? Or are they meant only for black Powder?

I shot a Uberti 1873 in 44-40 for a number of years when I was into Cowboy Action Shooting. I shot both "full power" Black Powder loads, factory loaded ammunition, and both cast and jacketed hand loads using modern smokeless powder. I paid strict attention to the data from my loading manuals and did not try to hot-rod the gun/ammo. I think as long as you stayed within factory load parameters you should, obviously, be fine. Personally I would limit anything in 44 Mag to 44 Special equivalent load levels. I don't think you will have any problems with factory loads in any of the other calibers as well. The action does have it limitations, but is still pretty strong. If you want a lever gun that will allow you to push the power envelope to higher levels like +P, then I would be looking for a Browning 92/94 clone, Marlin, or Winchester designs. I am not knowledgeable about the specifics of the newer Henry action designs so will not comment one way or the other. ymmv.

I was thinking of getting the 357 mag version

Same as before. Any standard pressure loads should be ok. I would stay away from any +P or +P+. Others experience may differ, but with older designs, I tend to be a little more cautious than some others. For example, I have some very fast 7x57, 120 grain loads that are very close, if not faster than some 25-06 MAX loads with the same weight bullets. I have no problems shooting those loads in a MODERN Model 70 Winchester bolt gun. I WOULD NEVER SHOOT THOSE LOADS in any vintage 1893, 95, 98 Mauser actions as I do not feel they would be safe. I might get away with it for awhile, but why run the risk?

Aside from the cleanup, shooting Holy Black in the old lever gun cartridges, especially at night is TOO MUCH FUN.

First, let me say that the 357mag load is absolutely great in a levergun caliber. 

I have 2 Rossi Model 1892 rifles, a 24" rifle and a 20" carbine, both in 357mag.   I also have 2 Uberti rifles, an 1873 24" Special Sporting rifle and an 1866 19" Yellowboy carbine, both in 45 Colt.  I don't recommend the Ubertis for a regular diet of full power 357mag as their toggle link actions were not designed for the kinds of bolt thrust that the high pressure magnum calibers produce.  Check out the thread entitled Lever Action in 45 LC? in this forum and look at my various posts discussing my Ubertis, the Bolt Thrust table, and my Rossis.