All custom vias which are part of the validVia list of the LEFDefaultRouteSpec constraint group will be considered as DEFAULT.
I'm not finding this to be the case. My techfile has
( "LEFDefaultRouteSpec" nil "LEFDefaultRouteSpec"
( M1 M2 M3 M4 M5 M6 M7 )
( M2_M1 M3_M2 M4_M3 M5_M4 M6_M5 M7_M6 )
and I'm still getting the error during globalDetailRoute
#ERROR (NRDB-158) There is no default via from LAYER M1 to LAYER M2 in RULE LEF_DEFAULT.
btw, I'm running Encounter 11.10