I have tried to import a collection of .SID files and various tracker files (.MOD, .XM, .S3M, .SC68), all in all about 58000 files (1 GB), mainly the High Voltage SID Collection. The rescanning of my music library folders, now including the new files, caused the importer to freeze (every time at 75806 of 95736 files scanned, 32480 new files added) and once I even got a System.OutOfMemoryException error in the log. The problem could be either the amount of files, or the basszxtune.dll not recognising a specific format (I found that .SC68 files are not imported), or a specific file in one of the folders, I don't know. I only know that without the chiptune/tracker folders the scan runs through without any problem. I have cancelled the process because nothing moved for an hour. Cancelling lead to another error message: A background process could not be closed. I restarted MusicBee as recommended and tried to scan my music folder again. This didn't improve anything, I couldn't import all of the tunes.
Now for the files that were actually imported: Playable were .MOD, .XM and .S3M files and scrobbling to Last.fm works for the files with proper tags and the appropriate duration > 30 seconds.
.SID files were imported as well, but they can neither be played nor scrobbled. Trying to play a .SID leads to an error message stating it's either an unsupported format or a broken file, which I can easily falsify: Using Foobar2000 with SID Decoder
caused no problem at all and the Audioscrobbler did scrobble the .SID tracks properly.