When I first got my 44 Spec calibered Open Top and 44 Spec 66 'Yellowboy' (2007) I bought 500 44 Spec and 500 44 Colt cases from Starline. Plan of attack was to load smokeless in the Spec's and black only in the 44 Colt cases mainly for ID purposes of knowing the SL from the black and so some sense of 'Old Timey' shootin with close to the org caliber and powder in the 44 Colts. Bought a Richard II about a year afterward in 44 Spec so the same procedure was followed. Worked, no problem, most times when shooting would only shoot SL loads, other times only black powder loadings. Had accurate loads for both powders, no big problems.
For some unknown reason, I started shooting more black than SL in them and soon quit loading smokeless in them. Wanted to shoot the 44 Specials with a little more steam, but couldn't, so purchased a Ruger 44 Super Blkhawk and Marlin 1864 Cowboy rifle chambered in 44 Mag. Now anymore the pre-1900 models get FF Goex black only topped with 200 grain Mav's in 44 Colt brass and the 44 Specials are shot threw the Ruger and Marlin using cast 240 grainers with harder lead, with some loadings a tad under 1000 fps and some 1000+. Makes for fun shooting all way around.
BUT to be true to the OP's first question, smokeless can be loaded safely in either revolver model as long as you don't exceed pressures that will tear it apart (neither are top strap models and even then aren't built to the ruggedness of a Ruger or modern Colt.) Keeping the fps/velocity under 900 too (which helps keep pressure down), follow loadings in manuals or publications, and suggested loadings from fellow shooters or on-line loadings as suggested here at CAS and both guns will eat em up with no problems. Word of caution though, always check any suggested loadings with manuals, powder company suggestions, etc as ya never know, what was typed may be in error or the guy typing has no care how he beats his gun or concerned about his safety. Not hittin on anyone here, just saying--better to play it safe. Of course pre-exhisting problems with the guns such as arbor fit, bolt/lead-cylinder bolt cavity timing, and other problems that are unique to these reproduction pieces need to be worked out if present. My OT needed arbor fitting and bolt/cylinder timing done (bolt coming up to soon). My Richards II just needed a little stoning of the inards. Both now are eatin up anything I stick in em and pop the primer!