Even if there were no job reductions between a NWA/DAL merger, a DAL new hire today would still be integrating with a NWA work force where the junior most DOH pilot is 8/27/2001. Regardless of how an eventual integration is handled with slotting, fencing, shuffling, oija boards, pistols at 12 paces, "cage of death", arbitration, etc., DOH is part of the formula and there could be some relative loss of seniorty.
There are considerable numbers of furloghed pilots deferring/bypassing at both NWA and DAL. Thier seniority is protected and when they return they come ahead of you. OTOH the combined airline would be a force to be reckoned with, and you have a number and are on the property, which is still way better than being on the outside looking in.
The sooner you get hired and get bodies beneath you the better. Also consider that even if there is a merger announced, it could take close to a year to consumate, and another year or 2 to actually integrate the operations. The snapshot date used for integration is waaaay off in the future, and are you are getting relative seniority in the mean time.
Being a new hire anywhere has an element of risk, however unless you have something way better going, the upside favors going to work a DAL.