If this is a home campaign, go for it! We presently don't have a huge amount of material on Canceri in ARPG (it's on the list from what I'm told, but it is not near the top of the list to do), and if you wanted to make your character a Cancerese Nerothian "Secret Policeman" Priest, the role you want to go for would be what are called Abjurers. These are religious hit-squads which act kind of like Inquisitors, and typically move around in groups of 3 (one Nerothian, one Nierite, and one Sarishan). They tend to wear obscuring masks, and are feared by much of Canceri as the enforcers of dogma. For more information, please see this product:
http://drivethrurpg.com/product/20781/T ... _45322_0_0Now, if this is meant as a Living Arcanis-Legal campaign character, I'm not sure the character concept will really work. As stated, Canceri is not a playable nation, and outside of Canceri itself the Dark Triumvirate is not worshiped. You probably COULD make a case for a character coming from the Hinterlands who follows a very Cancerese-like worship of Neroth, but by and large even the chaotic religious area of the Hinterlands finds Cancerese (especially the Nerothians) repellent.
Neroth is, however, not exclusively worshiped in Canceri, which means you do not have to be tied to that nation! One of the first "commandments" of Illiir in the Canticle (the holy book of the Pantheon of Man) is that "All Gods must be given their due", and this includes Neroth. In Coryan, Neroth is worshiped as the God of Disease and Medicine (not necessarily healing, I should point out, but medicine), as well as being the caregiver of the mentally infirm. They perform burial rights and are also the undertakers and morticians, and are given the bodies of the dead after the Beltinian clergy deals with the souls of the dead. By and large, Neroth is still thought about with fear and a little disgust by the 'common folk', mostly out of the ancient fear of death and the dead (and the pollution it is thought to bring), but he is venerated there. The most prominent Nerothian Holy Order in Coryan is the Order of the Deathbringers of Neroth, who are almost the most "Lawful Good" order out there, believing that it is there Neroth-given mission to hunt down all evil in the world due to a mistake made by their Lord in killing Illiir (who got better) in a very Pandora's box-like myth. It should be noted that while the Mother Church of Coryan isn't necessarily AGAINST the existence of undead (or the raising of the dead as minions), it is considered rather gauche and is a continual sticking point between the followers of Beltine and Neroth, and such activities would almost certainly be frowned upon by the common folk.
In other nations, Neroth is viewed in much the same way as in the Coryani Empire, with greater or lesser influence being given to some of his more extreme aspects (read: undead and disease). Milandir is probably the LEAST tolerant of Neroth due to their history of war with Canceri, and the worship of Neroth is pretty much exclusively restricted to his role as mortician and undertaker with Beltine taking over most of his medicinal roles.
Also of note: Neroth is not the God of Suffering, but the Lord of the Dead, Disease, the Body, and to an extent the Mind. Anshar is the comforter of the Suffering and the patron of the outcasts.