I am not very familiar with the UA plugs. SF supports most Direct X, VST 2/3 32 and 64 bit . I think Pro13 has ARA2 support like the current Pro 14 publication.
I recall the UA plugs needing a controller app or wrapper to run them, I know little about that
In this context, <.dll> files are generally VST files. If they are 64 bit VSTs confirm they are in a "Program files" folder. If 32, "Program files (x86)"
Either way, confirm the pertinent folder(s) are selected in "Options> Preferences> VST Effects> VST Search folders"
According to the UA website, they are 64 bit VST compatible. No mention of SF or Vegas.so they may not work. Contact UA support and ask if they are supposed to be compatible with Magix apps (SF and Vegas).
Your comment re 64 bit was helpful. I scanned the UA 64 bit plug-in folder and the 64 bit plug-ins now can be viewed in the plug-in chain but will not operate. When activated I get the error message "An error occurred while loading a plug-in. The plug-ins do not support the track's media type."
I assume there is no need to contact UA at this point?
If it works with PCM files and you have lossy file types (MP3, AAC, ect) SF can build proxy files (PCM) if so selected in "Options> Preferences> General"
In a search and perusal of the UA forums, I cannot find a definitive answer. I urge you to still contact UA support.
FWIW, I have used UA vintage hardware. but not the plug-ins .