More like the officially licensed novels, not fan fiction. Some aspects of licensed Treklit were used as background for ST09 and STD, and probably ENT S4 when the Reeves-Stevenses were involved.It has the same power as fan fiction in another words. Star Trek writers can copy elements into their stories but does not make the fan fiction canon by doing so.
But professional writers and producers avoid reading fan fiction (as well as unsolicited scripts or story ideas) as a matter of policy, to avoid liabilities such as accusation of stealing somebody's idea.
Kor