Can I use the djs-1000 with the ddj-1000srt?

Without pro link you would have to hook it up as a line in but not as a linked unit.  If you want to play back samples with it then just go line in.

So I need to run Ableton and Serato at the same time?  I'm trying to use the djs-1000 in combination with live tracks from the ddj-1000 srt. Can I only use samples from the djs? I would love to be able to add elements to the song. Is that not possible?

I think Jay got a bit confused with his answer; you can run the DJS with the DDJ, but it's not recommended you hook it up in such a way as to create an audio loop-back which can cause a feedback loop. In other words, you can set it up either to play samples from the unit itself into one of the channels on the DDJ so you can control the volume and apply effects, or you connect the DJS post-output of the DDJ and are able to capture samples from the performance, but then would have no control over the levels.