Prior to America's entry into WWI the Zimmerman Telegram was one incident that helped push America to declare war against Germany and join the Allies.
While Mexico never fought against the US, so was this even a possibility?
I don't know how strong Mexico was at the time. Everything I have read says it was not able to sustain a war of any kind against the US. And considering how far Germany was: would there have been any way for Germany to give aid?
The telegram seems more a ruse on the US than a way for Germany to incite Mexico to wage war on the US and distract the US from the war in Europe.