Compiling the shader below with the options:

dxc.exe -spirv -E main -T hs_6_0 -fspv-target-env=vulkan1.1 bad.tesc -Fo bad.tesc.dxc.spv

Gives the error:

bad.tesc:14:46: error: patch constant function parameter 'Inside' unknown
                                   out float Inside[2] : SV_InsideTessFactor)
                                             ^

Compiling to DXIL occurs without error:

dxc.exe -E main -T hs_6_0 bad.tesc -Fo bad.tesc.dxil

bad.tesc:

struct VSOutput
{
    float4 f4Position : SV_Position;
    float3 f3Color        : COLOR;
};

struct HS_CONSTANT_DATA_OUTPUT
{
    float Edges[4]  : SV_TessFactor;
};

HS_CONSTANT_DATA_OUTPUT ConstantHS(InputPatch<VSOutput, 1> p,
                                   uint BlockID        : SV_PrimitiveID,
                                   out float Inside[2] : SV_InsideTessFactor)
{
    HS_CONSTANT_DATA_OUTPUT Factors;
    Factors.Edges[0] = 2.5;
    Factors.Edges[1] = 4.25;
    Factors.Edges[2] = 5.75;
    Factors.Edges[3] = 7.5;

    Inside[0] = 6.75;
    Inside[1] = 7.25;

    return Factors;
}

struct HSOutput
{
    float4 Position : POS;
    float3 Color    : COL;
};

[domain("quad")]
[partitioning("fractional_even")]
[outputtopology("triangle_ccw")]
[outputcontrolpoints(1)]
[patchconstantfunc("ConstantHS")]
HSOutput main(InputPatch<VSOutput, 1> inputPatch, uint uCPID : SV_OutputControlPointID)
{
    HSOutput Out;
    Out.Position = inputPatch[uCPID].f4Position;
    Out.Color    = inputPatch[uCPID].f3Color;
    return Out;
}

Related: KhronosGroup/glslang#1553