According to the Routeing Guide, Burnley Manchester Road and Manchester Victoria share a common routeing point, Manchester Group, which means valid routes are by the shortest route. They are also valid for use on direct services.
I cannot find a mileage for the Todmorden Curve in the National Rail Timetable, but I think we can safely assume it is shorter than via Hebden Bridge.
Manchester Victoria to Hebden Bridge (table 41) and Hebden Bridge to Burnley Manchester Road (table 41) is a total of 36.25 miles (23.5 + 12.75)
Manchester Victoria to Blackburn (table 94) and Blackburn to Burnley Manchester Road (table 41) is a total of 37 miles (24.5 + 12.5)
There may be an easement, I haven't checked.
The routeings for available tickets are 'Any Permitted', 'Via Preston' and 'Via Todmorden'.
Via Preston costs more than Any Permitted, and Via Todmorden costs less. I think therefore it is implied that Manchester Victoria-Blackburn-Burnley Manchester Road is fine, but on a technical level I suspect it may not be.
As an alternative, might I suggest Manchester Stns to Accrington. It's about the same cost and the presence of a 'Via Bromley X' fare means there is definitely a permitted route via Blackburn (without having to go to Preston). There's still no guarantee of it being valid via Hebden Bridge, but it's not likely to be a big concern.