At first, it looked like it was working, but then the merging of the video and audio streams failed. Bummer…
After playing around with ffmpeg for a while, I got the following error message when trying to merge the streams:
Malformed AAC bitstream detected: use the audio bitstream filter 'aac_adtstoasc' to fix it ('-bsf:a aac_adtstoasc' option with ffmpeg)
Using the suggested option resulted in a successful merge.
Out of curiosity, I added this option as post-processor option to my youtube-dl command and, voila, it worked!
youtube-dl --postprocessor-args "-bsf:a aac_adtstoasc" VIMEO_URL