Assess vendor due diligence

It has always been best business practice to ensure due diligence in dealing with any contract situation. However, there is always the one that got away. Without going into extreme details, through an RFP process, analysis and investigation was conducted leading us to settle on one particular vendor's product. This application would need minor customization and the overall cost of implementing it would be very assumable. All references were clearly researched and documented. After the contractswere signed and my team began the initial project disucssions for the planning I discovered that the vendor had "lied" about it's availability on Oracle - in fact they were only in early beta testing. I put a halt to the project, presented it to the senior management and to our legal staff but I was out voted and they continued on with this vendor who was clearly in breach of contract. All the scenarios I supposed and informed the others have since come to pass and this vendor is like a sewer stink that won't go away. My staff and I are obliged to work with them and we have attempted to make good out of bad. But it still stinks. We are still "sinking" money into the project since this is now a political boondoggle. So, how much due dilligence is required if all was done as prescribed? Can you ever fight the corporation's bad decision in going forward? I've ensured that my staff and I have not had any of this stick to the team but it smells and looks bad just the same. I viscerally react every time this vendor is mentioned. Due dillegence, right; it becomes CYA instead . . .