Hmmmm no, in fact strategic wise that would be a horrible move.
For starters as far as I know Raiko doesn't have an army. They use the United Forces army, which isn't his personal army. Kuvira is an absolute ruler, she has complete control over her entire army and can move it as she sees fits solely based on her own judgements. Her army is her plaything.
The UF is completely different. It's an army that consists out of people from all nations and as a result all nations have a say in it. It's not an army Raiko should be able to command on his own whims like Kuvira, he needs to discuss the movements of the army with other people. Compare it to the NATO, it's an army that transcends the level of a country, it's an international army. As a result making it move goes much slower than Kuvira making her own troops move.
Secondly the nature of the two armies are very different. Kuvira's army is a conquerors army, an offensive army. She used it to take control over the entire Earth Kingdom. The UF is an army of defenders, a defensive army. When Amon took over RC, they were there to free it as the city got taken over by terrorists/anarchists. The peace in the Earth Kingdom however was restored by one of their own. It wasn't an outside force that tried to throw the kingdom into chaos, but an inside force who restored peace. Many people support Kuvira atm, so just haphazardly marching an international army in there under the flag of 'liberation' would just be considered by many citizens as a pitiful excuse to conquer the land. Diplomatically seen that would be an extremely bad move as long as Kuvira is considered a hero by most people. Even if they would beat Kuvira like that, the vicious cycle would continue and even worsen as it's not like the Earth Kingdom citizens are going to listen to an invading army that just threw down the one person who brought order to their country, order that was instantly lost after she was beaten.
Thirdly it's unclear to which degree the UF uses or can use the railroad network, but I think it's safe to assume that Kuvira has control over most of the network that crosses the Earth Kingdom. This allows her to quickly deploy her troops anywhere, this in contrast with the UF who might not have that luxury.
Fourthly it took Kuvira three years to unify the Earth Kingdom and then the UF need to do it in a few days? Also what point would there be in starting to take few territories back at the edge of the kingdom? If they start a war for control over territories, this war could be dragged out for years, which is the last thing they all want. Also they would be forced to leave troops there to keep it under control, so the further they would go, the weaker they would become. Kuvira has by far the advantage.
So no it would neither be smart, helpful nor would it possibly even work. Zaofu had a large amount of autonomy and was clearly resisting Kuvira, so they could use that as a viable reason to justify deploying troops there, but it's much more tricky for the rest of the Earth Kingdom.
