I added StyleCop.Analyzers to my project and managed to manually add a ruleset file to the csproj.

Creating the project

md test
cd test
dotnet new console

The ruleset file

<?xml version="1.0" encoding="utf-8"?>
<RuleSet Name="WebDAV-Server Ruleset" Description=" Rules for the WebDAV-Server project" ToolsVersion="15.0">
  <Rules AnalyzerId="StyleCop.Analyzers" RuleNamespace="StyleCop.Analyzers">
    <Rule Id="SA0001" Action="None" />
    <Rule Id="SA1101" Action="None" />
    <Rule Id="SA1300" Action="None" />
    <Rule Id="SA1309" Action="None" />
    <Rule Id="SA1400" Action="None" />
    <Rule Id="SA1503" Action="None" />
    <Rule Id="SA1600" Action="None" />
    <Rule Id="SA1633" Action="None" />
  </Rules>
</RuleSet>

The project file

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp1.0</TargetFramework>
    <CodeAnalysisRuleSet>test.ruleset</CodeAnalysisRuleSet>
  </PropertyGroup>

  <ItemGroup>
    <AdditionalFiles Include="stylecop.json" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="StyleCop.Analyzers" Version="1.1.0-beta001">
      <PrivateAssets>All</PrivateAssets>
    </PackageReference>
  </ItemGroup>

</Project>

The stylecop.json file

This file is malformed, because comments aren’t allowed in the project.json file.

{
  // ACTION REQUIRED: This file was automatically added to your project, but it
  // will not take effect until additional steps are taken to enable it. See the
  // following page for additional information:
  //
  // https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/master/documentation/EnableConfiguration.md

  "$schema": "https://raw.githubusercontent.com/DotNetAnalyzers/StyleCopAnalyzers/master/StyleCop.Analyzers/StyleCop.Analyzers/Settings/stylecop.schema.json",
  "settings": {
    "documentationRules": {
      "documentInternalElements": false
    },
    "orderingRules": {
      "usingDirectivesPlacement": "outsideNamespace"
    }
  }
}

Commands

dotnet restore
dotnet build

Output

Microsoft (R) Build Engine version 15.1.545.13942
Copyright (C) Microsoft Corporation. All rights reserved.

Program.cs(1,1): warning SA1200: Using directive must appear within a namespace declaration [C:\temp\test\test.csproj]
CSC : warning AD0001: Analyzer 'StyleCop.Analyzers.SpecialRules.SA0002InvalidSettingsFile' threw an exception of type 'System.TypeLoadException' with message 'Could not load type 'System.Runtime.Serialization.Formatters.FormatterAssemblyStyle' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.'. [C:\temp\test\test.csproj]
  test -> C:\temp\test\bin\Debug\netcoreapp1.0\test.dll

Build succeeded.

Program.cs(1,1): warning SA1200: Using directive must appear within a namespace declaration [C:\temp\test\test.csproj]
CSC : warning AD0001: Analyzer 'StyleCop.Analyzers.SpecialRules.SA0002InvalidSettingsFile' threw an exception of type 'System.TypeLoadException' with message 'Could not load type 'System.Runtime.Serialization.Formatters.FormatterAssemblyStyle' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.'. [C:\temp\test\test.csproj]
    2 Warning(s)
    0 Error(s)

Time Elapsed 00:00:02.02

Expected output

Either a good error message that the project.json is invalid or accepting the json file and not throwing the TypeLoadException

Additional information

The error doesn’t appear when run from inside VS 2017.