Not quite "new hire" seniority. The TA says "will be treated as junior to all pilots who are on the seniority list on the effective date of this letter". That would imply that they would be treated as senior to pilots who where not on the list ( i.e. 3rd listers).
Also, they retain and accrue their longivity for benefits, retain their AWA position, are not required to serve probation, but may be required to forgo recall to the West operation for 18 months.
BTW, the most senior West furlough ( furloughed 5-1-09)was hired in 2004, over a year before Colello's recall. The most senior furlough from 4-1-09 was hired 8-16-04, 9 months prior to the merger and about three years after his previous furlough from USAirways post 9-11, originally hired east 11-99 ( he is one of the Addington plaintiffs). The most junior who was on the list prior to the TA, Odell, was furloughed 10-1-2008 (and has 125 furloughs above him) although east furloughed pilots who took West recall and are by every measure junior to him, were allowed to move back east and keep a job.
So, if our scenario ever comes to pass, be certain their will be a grievence filed if the hypothetical West pilots are not place senior to those who were not on the list " on the effective date of this letter".