Hello Fabian
Actually, you can use them, and they will work fine. The only issue you will have, as stated in the less, is that a host may receive and accept a frame that belongs to a different multicast group. If this happens, the host will have to decapsulate the frame and examine the destination IP address in the IP header. If it is not to a destination multicast address to which the host has joined, it will simply be discarded.
So rather than discarding the frame, it will actually be processed up to the 3rd layer and discarded then. So it is adding more processing to the host. This will only be a problem under extremely high multicast traffic. Otherwise in most situations you probably won’t notice a difference.
Now having said that, best practice dictates that you should not uses these addresses simultaneously in your network to avoid any unnecessary processing by the hosts.
I hope this has been helpful!
Laz