When another craft works a Rural Route are they truly another craft?
Yes. They do not become a member of a different craft whenever management assigns them to work belonging to a different craft.
Employees are classified by designation code (See Article 7). The designation code is associated with the craft to which they belong.
Dual appointments (See ELM 348) were once a thing, but to my knowledge, no longer coexist with any rural designation (7x).
Bargaining unit work is determined to the appropriate bargaining unit (union). That workload is then protected by inclusion and exclusion causes within no less than Article 1 of all national agreements.
Other than the 90 day wonders substitutes come from a contractual agreement. Does a union have the ability to set rules outside of its craft?
The union cannot negotiate rules for other bargaining units, but it is the gatekeeper for who can perform its bargaining unit's work as well as what labor its bargaining unit members can perform.
For example, for the NRLCA:
1) City employees performing rural work is a violation against NRLCA because that workload and the wages/hours/benefits that result from processing that workload belong to NRLCA bargaining unit members, not NALC bargaining unit members.
2) Rural employees performing city work is a violation against NRLCA because that workload and the wages/hours/benefits that result from processing that workload have not been negotiated by the NRLCA. In this case, the employer is unilaterally sidestepping the union's right to bargain by assigning wages and benefits to that rural employee who is crossing crafts.
The NRLCA is mistaken when they argue that only the NALC can grieve when rurals cross craft lines. A violation of #1 for NRLCA is a violation of #2 for the NALC, just as a violation of #2 for the NRLCA is a violation of #1 for NALC.
If this weren't the case, then management is not sincerely bound to either union's Article 1, "union recognition" clauses.
Is it possible to pursue paying CCA’s 3 times over time rate to work a Rural Route?
Whatever number their golden goose pops out is immaterial. While the employer will choose whatever amount they unilaterally deem justified, rights to the workload were never surrendered and the wage was never negotiated by the bargaining unit recognized at the national level.
If this is not really happening then it should not be a problem. If substitutes for us are not being hired it is a penalty. Possibly winnable in arbitration?
One route the union could go to stop craft crossing is agree to allow non-craft employees to do the work, but only at the national minimum wage.
How many city employees would vault the craft line at $7.25 an hour?
I'd hope that the NRLCA could defend a simple definitional bargaining unit work argument, but since they can't even follow simple certified correspondence requirements within their own constitution, I'm not holding my breath.