Yes it is spam and no there isn't much that can be done.
A ) The admin can turn on admin verification so new members need approval to join.
B ) The admin can go thru the members list and remove them as they join (which I do on my site, usually 5 or so a day)
Have a look at the members list and filter by members post count - you'll find there are hundreds of spammers that have joined and never posted.