If they're listed in the GnuPG manual as "well functioning key servers", you can be sure they synchronize with each other (and are part of the whole set of synchronizing key servers, which are far more than 100). Any of them can be used to arbitrarily, and you will nonetheless get hold of all keys.
This list seems to be a little bit outdated, at least the key server hkp://blackhole.pca.dfn.de
is not available any more for some years now.
It is generally recommended to use the key servers in the SKS Key Server pool, which synchronize especially fast and you do not have to rely on the availability of a single server. Lots of the servers in the list provided by the GnuPG manual actually are part of the SKS pool and will (chosen randomly) also be queried from time to time, if you use that pool.