Srikantha was a famous Shaivite acharya from South India of the eleventh century who propounded the Shiva Advaita philosophy which is very similar to Ramanujacharya's Vishistadvaita philosophy. Is Srikantha regarded as an incarnation by his followers?
First of all, Srikantha Sivacharya, aka Nilakantha Sivacharya, has very few followers. The Shaiva Siddhanta sect is divided into three sub-groups: mainstream Shaiva Siddhantins, the Shrauta Shaiva Siddhantins, and the Shaiva Siddhanta Church. Now the Shrauta Shaiva Siddhantins, who form a tiny minority within the Shaiva Siddhanta sect, are the ones who follow Srikantha Sivacharya and Appayya Dikshitar.
But yes, they do consider Srikantha Sivacharya to be an incarnation of Nilallohita, one of the Rudras. here is what this Shrauta Shaiva Siddhanta website says:
The Acharya was born in 2044 Kali Era or 3100 BC equivalent to Swabhanu Telugu year, Chaitra month, Sudha Dasami, Pushyami star, Monday, Karkataka Lagna at Srikaleswaram, Warangal in Andhra Pradesh to Gowri and Visweswara, Maheswara Aradhya parents of Bharadwajasa Gotra with the blessings of Sri Kaleswara Swamy with Nilalohita Rudramsa under a boon granted by Lord Siva. This is stated in Nilakanta Vijaya Mahakavyam, written by Nagalinga Sastry garu in Sanskrit as under:
Chatu Chatwadi Rimsa Datta - Sahasra Dwitayamasu
Kalou Varsheshu, Vrutteshu Swabhanu, Subha Vatsare
Maasi Chaitra Valakshye - Pakshe Atha Dasamee Tithou
Pushyamyam, Indu Varecha, Lagne Karkata Kandaye
Gurou Karkat Karasisthite - Kuje Meenam Gatepiva
Meshe Ravou Budhayute - Vrushe Mandayute Kavou
Abhinandya Shrutam Jatam - Sannibham Jata Vedasaa
Gowri Visweswarou Dhanyou - Bhootwa Muda Mavapatu
He was born in Swabhanu Telugu year in Cancer Lagna with Jupitor and Moon there in, Mars in Meena 9th House, Sun and Mercury in 10th house Aries and Saturn and Venus in the 11th House Tarus. When Lord Siva along with Parvathi were holding court in the Hiranya Mantap in Kailash, with Hari, Brahma and other celestial Gods, Narayana requested Siva to send a scholar to propagate Siva Bhakti and to clearly explain the truth in Vyasa Sutrams to the people on the Earth. Siva stated, that since the influence of Maharshi Vighanas and Badari who were sent earlier to propagate Siva Bhakthi is fading away, He is sending Nilalohita Rudra to take birth on Earth to drive away the insanity of the people under the preachings of the Mayavadis and to propagate Srouta Sivaradhya Sampradayam.