Can a ninja learn a jutsu that lies outside of their own alignment? Quite some time ago I got into a... minor argument regarding whether or not a ninja could in fact learn a jutsu to which their natural alignment was not geared toward. I felt you could, but it would be more difficult than it would be for someone whose natural alignment lies with that element. The person I was discussing it with did not. They felt it was impossible for a ninja to learn a jutsu outside of their natural alignment.

I stopped reading Naruto quite some time ago but I was wondering if anything came up that answered that question in one way or another?
It is not impossible, but it is rather difficult to do so. All Jounin level ninjas have to master more than two elements. Kakashi can perform 3 different element jutsu: Lightning, Fire, Earth. Yamato can do Earth and Water. Sasuke can do Lightning and Fire.

Even if someone has a natural inclination towards one element (Sasuke towards Fire), they can still perform other elemental jutsu (Sasuke can perform Chidori, a Lightning Release).