Are there Advaita Vaishnava sampradayas also?
There is a good section of people who believe Adi Sankaracharya himself was a Vaishnavaite and that being an Advaitin and a Vaishnava may not be mutually exclusive. This topic has been at the center of some of the most intense, sometimes cordial, sometimes downright nasty, debates online. I don't have any intention of getting in to any debates here with people throwing vakyas, bhasyas and all things at each other.
But then there are people within advaita tradition that focuses purely on devotion to Narayana but ultimately they do believe the Nirguna concept being the end all.
Here's an interesting read:
whether Shaivas and Shaktas think themselves as part of Advaita's pancayatana or they also oppose Advaita and have separate sampradayas?
I had asked a similar question here and am still waiting for an answer.
Most Shaivas and Shaktas certainly do not link themselves to the Advaita samparadaya of Adi Sankaracharya. They might have their own advaitic siddhantas, but many of them do not even consider Veda vedanta as authoritative above their agamas or other texts. Lingayats are the first to come up in my memory that fit that criteria. There will be shaivaites and shaktas within the Advaita sampradaya but then I am sure they are in the scope of this question.
Here are some pages already on Hinduism.stackexchange that detail out some of the issues that relate to Shaivism and Vedanta.
Which Shaivite sect believes God is the operator of the Universe but not the source?
What commentary on the Brahma Sutras does the Saiva Siddhanta Church support?