Is legal GPL3 / Free Code "SPARK" ?

We can use the spark libraries, to make some arrangement?

is it legal?

We have read and understand that if. 

To all this, when we have your application, we would like to put on the cover, references to "Openfire" "Spark" etc..

http://community.igniterealtime.org/thread/39777

http://es.wikipedia.org/wiki/Openfire

http://www.igniterealtime.org/projects/spark/