To reproduce:
1. Open attached project "New Unity Project 2.zip"
2. Open shader graph "Graph.shaderGraph"
3. In Sample Texture 2D Texture(T) field, select GraphTexture (this is a render texture)

Expected result: render texture is added
Actual result: render texture is not added

Reproduced on: 2018.1.0b10 2018.2.0b1

2018.1.0b10 with Render-pipelines.high-definition textures are always pink

MacOS 10.13.4
iMac (Retina 5K, 27-inch, 2017)
CPU: 3,4 GHz Intel Core i5
GPU: Radeon Pro 570 4096 MB

Adding Texture 2D Asset node and connecting it to Sample Texture 2D Texture(T) field using the same texture everything works as expected.
Also reproduces on windows 10.