I have an old Roland MC50mKII sequencer, and disks with tons of midi songs on them.  I also have a UM-ONE MIDI USB cable.
 
If I run that cable from the MC50 to my computer, can I transfer the midi data to MC7?  And if so, I assume I would need Cakewalk TTS-1 activated to hear the sounds?

I don't know anything about the synth BUT.... if you can off load the data to a disk or thumb drive, or a direct to the computer download, you can create a new folder and save it all there. From inside of MC7, you should be able to load those files by simply navigating to them.
 
Most all midi devices that can save files internally, have some way of exporting the files.  Follow the recommendations for your device.
 
You would then assign the proper soft synth to play them.

hi
you have to install the driver (UM one) on your OS 
playback the files on the MC50MKII and record them in your MC.
BTW .I am using the sound machine AC1200 from technics with all the possibilitys ( 25 years old!!!)
There is no need to use the TTS but you can,  
have a great run
ries