Yes, but you will need a diverter.  The Graf rain barrels are closed systems, meaning that there is no screened inlet like some other rain barrels.  It is best to use a diverter that is directly plumbed to the rain barrel.  Exaco does have two diverters (one circular, one rectangular) that insert into a hole cut into your downspout and then travels down a tube that inserts into a hole cut into the rain barrel.  When the rain barrel is full, any superfluous water continues down your downspout.  The barrel has no overflow piping to worry about.  The diverters are sold separately from the rain collection tanks.