This thread has been bothering me because this is an issue I explored some time ago when designing/deciding on a template. There are statements offered in the posts above that are incompatible with the results of my earlier tests. So - I repeated, in an abbreviated form, many of those tests today. I am on Europa. My results continue to suggest that:
1. Wearing the Conjuror's Talisman does not affect the damage inflicted on you by another player whatever slayer weapon they are using. No difference at all.
2. Wearing the orc "Big Majik Flippers" to assume orc form, does not affect the damage you inflict on a player wearing the Conjuror's Talisman. No difference at all.
3. Wearing the orc sandles (above), increases the damage taken from a player wielding a Repond slayer by approximately 25%.
I would very much welcome someone repeating these tests and either corroborrating or challenging my conclusions. It would be particularly interesting if results proved to be different on different shards.
PvM is entirely another matter and wearing/using an Undead slayer around Baracoon could well be problematic. I haven't tested the Orc Brute but suspect it is treated as essentially a PvM interaction, not PvP. I haven't tested this personally at present.