Well, though it has been underplayed in the sense I haven't seen it reported in the English press, Aslan Byutukayev (essentially lineal successor to Khattab, Basayev etc and behind the 2014 Grozny attacks) swore allegiance to Isis in June already.
I also noted from Robert Fisk's coverage that the first strikes the Russians carried out were against Turkmen/Chechens....essentially people who would be fighting in the Caucasus/ committing terrorism there. This was his explanation for the choice of the first strikes when they started in earnest.
It would make sense in the context of the previously posted article suggesting Russia's end game is strategic defeat of Al Qaeda and Isis, bearing in mind Isis now encompass the Islamists seeking the Caucasian and Ichkerian emirate.
Edit: I see the state department added them by name, as the Caucasian unit of Isis on 29th September this year.
Designations of Foreign Terrorist Fighters
And they cite a sept 2nd attack in Dagestan:
"The Islamic State of Iraq and the Levant – Caucasus Province (ISIL-CP) became ISIL’s newest regional group on June 23, 2015 when the spokesman for ISIL leader Abu Bakr al-Baghdadi released an audio recording accepting the sworn allegiance of the fighters of four Caucasus regions – Dagestan, Chechnya, Ingushetia, and Kabardino-Balkaria. The statement also appointed Rustam Aselderov as the emir of the new ISIL-CP. On September 2, 2015, ISIL-CP claimed responsibility for an attack on a Russian military base in Magaramkent, southern Dagestan, which resulted in the deaths and injuries of a number of Russian citizens."