Yes, you need to pass in -S erupter:all in order to have them detected as a Block Erupter
Must I do it or may I leave them being recognised as Icarus? Does it change anything from practical point of view?
Using the erupter driver gives you: correct hashrate, timings, and identify function.
With icarus timings, you
might lose some hashing time until it calibrates, but I've tried to minimise that.