Nevermind! I solved my own problem.
In the shader that I was using, the lerp function was float3 = lerp(float3, float4, float)
and unity's auto-translation into a PlayStation-friendly shader didn't know how to handle that float4. So for me, because my function didn't need the alpha value, I changed the line to float3 = lerp(float3, float4.rgb, float)
and it complied with the more strict arugment rules for PS4 shaders.
The root of the issue is that the lerp function is simply not as flexible when building for PS4, and you need to be more explicit when feeding it arguments. I wonder if your solution was similar.