Where helping the Saudi led coalition was somewhat ambiguous before under both agreements with allies like Saudi Arabia and the resolution passed nearly unanimously before Afghanistan. What this resolution does is to EXPLICITLY say that that resolution does NOT and can NOT be used to justify US involvement in the war in Yemen.
The US role in the Obama administration was far more complicated, where the Pentagon helped refuel SA coalition airplanes involved in attacking Yemen. Meanwhile, Secretary Kerry worked with Zarif to get the Shiite rebels to agree to various ceasefires and to begin diplomacy in Kuwait. It was the Saudi backed Hadi, possibly pushed by the UAE, who refused both the ceasefires and diplomacy. (To make things more complicated, Hadi, the deposed former President of Yemen who has been in Saudi Arabia for most of the war, is currently under house arrest in Saudi Arabia) http://www.aljazeera.com/news/2017/11/yemen-president-hadi-house-arrest-riyadh-171107082638642.html This article shows the complexity of the proxy war going on here.
As to war crimes, the UN and criminal court, not our Congress determine that. There have been calls to consider at least some of the SA coalition attacks to be war crimes. Various groups including Human Rights Watch and Amnesty International have made the case that war crimes were committed and the UN has a resolution to send a team to investigate - http://www.bbc.com/news/world-middle-east-41446342 Even in the Obama years, there was a question as to whether Americans could risk being accused of war crimes. What is clear is that Yemen, always a poor country, is now a catastrophe.