How to reproduce:
1. Open the attached 'project-1184463.zip' project
2. Open Package Manager and enable preview packages
3. Inspect 'Vector Graphics' dependencies
4. Remove the 'Unity UI' package
5. Observe the Console window

Expected result: no errors are thrown in the Console window
Actual result: errors are thrown in the Console window

Reproducible with: 2019.2.6f1, 2019.3.0b4, 2020.1.0a4 (preview.2 - 2.0.0, preview.5 - 2.0.0)
Could not test with: 2017.4.32f1 (Package Manager not available), 2018.4.9f1 'Unity UI' package is not listed in the 'All packages' list

One of the six errors: "Library\PackageCache\com.unity.vectorgraphics@2.0.0-preview.5\Runtime\SVGImage.cs(3,19): error CS0234: The type or namespace name 'UI' does not exist in the namespace 'UnityEngine' (are you missing an assembly reference?)"

Note: installing the 'Vector Graphics' package in 2019.3.0b4 or 2020.1.0a4 on a new project produces two more errors:
1) Library\PackageCache\com.unity.vectorgraphics@2.0.0-preview.5\Runtime\InternalBridge\VectorImageBridge.cs(88,25): error CS0117: 'Vertex' does not contain a definition for 'settingIndex'
2) Library\PackageCache\com.unity.vectorgraphics@2.0.0-preview.5\Runtime\InternalBridge\VectorImageBridge.cs(128,36): error CS0029: Cannot implicitly convert type 'UnityEngine.UIElements.Vertex[]' to 'UnityEngine.UIElements.VectorImageVertex[]'