Hi Alex,
The BGP Next-Hop address tracking features in IOS is to minimize the “Dataplaneconvergence”time for BGP prefixes for the dual-home environment where in any case that on of link is down, (in IOS) all the impacted BGP FIB enteries will be redirected to a valid path without requiring per FIB entry operation i.e. IGP convergence and later BGP NOTIFICATION to update change in next-hop. Insted, IOS BGP NEXT-HOP TRACKING monitor the loopbacks and trigger immediately BGP NOTIFICATION without waiting for IGP convergence.
I'm not fluent in rpd JUNOS but have you try simulate the dual homing scenario using Juniper devices. Does JUNOS rpd for BGP still inherit the BGP scanner scan-time/Hold time - 60seconds?