I'm not sure what they wear. I imagine different people choose different things. Necromancers can influence dreams as well as other aspects of a person's life. Voodoo is a form of necromancy.
Example, true and interesting little story:
Jim Williams, a prominent antique dealer in Savannah, GA., (the subject of the book/movie Midnight In The Garden of Good and Evil,) was arrested for the murder of an employee/companion of his in May 1981. Jim Williams, hired a voodoo priestess, to influence the outcome of the trial. She also put a curse on the prosecutor. During "dead time," which lasts one hour,(30 mins before midnight for good and 30 minutes after midnight for evil,) she went to the cemetery where he was buried, (Bonaveture Cemetery.) She took some of the soil...one minute before midnight for doing good spells and one minute after midnight for bad spells. The guy Williams murdered liked his whiskey, so she put a bottle of it on his grave to tempt his spirit to come out. Though Jim Williams was convicted in the first trial,information of mishandling of evidence was sent in anonymously, which won him a mistrial. Second trial: Convicted again, yet he verdict was overturned by the GA Supreme Court and another trial was ordered. Third trial: Minerva (the voodoo priestess went around throwing graveyard dirt on the doorsteps of Jim Williams' enemies, and the trial ended in a mistrial. Fourth Trial: Jim Williams was finally acquitted. When Williams was retried the 4th time, he became the only person in Georgia history ever tried for the same murder four times.
Here's the irony of it all: He spent 9 years trying to "beat the wrap." Seven months after being acquitted, he died, of a heart attack, in the same room in which he shot his companion. Now, he is spending eternity, buried in the same cemetery as the guy he murdered. Both are buried in Bonaventure, the Garden of Good and Evil.
So, yes they can influence dreams, and lives. I don't know if you are just having dreams, from your subconscious or not. I wanted to tell that story, because people that practice necromancy for personal gain, usually end up getting a bad deal. I'd stay away from those people, for sure.