Half-Life: Source materials not visible in Hammer++ texture browser

[The Tiny Desk Engineer]

I'm trying to make a map using Half-Life assets, so I mounted Half-Life: Source to TF2, and after some brief trouble caused by me not realizing VPKs needed to be mounted separately from mod directories, I was able to get all the assets properly showing up in-game when loading up various HL:S maps. However, In Hammer that was a different story. After I got things working in-game, I opened Hammer to see that all of the HL:S materials are showing up as missing textures. Models and sounds were working as expected, but all the textures were missing. I was able to get the textures to show up by switching from Hammer to Hammer++, but when I tried to use those materials myself, I noticed that none of them were visible in the texture browser. Searching the halflife folder where all of HL:S's materials are stored returns no results. There are, strangely, some textures that do show up in the browser, but under different paths, and those ones don't show up in the 3D view which defeats the whole point of all the work I've done. Anyone have any idea what's going on here?