Can't display transparency via Render Texture on Raw Image

I have a simple standard 2 camera setup to display an effect on top of everything.

It's the usual rig with the main camera having its culling mask to ignore the effect layer, and a secondary camera that captures only the effects layer, has a higher depth setting and clear flags set to depth only, and renders into a render texture which is placed in a screen sized RawImage (The render texture may not be a part of the standard rig, but is required in my actual project as I have multiple cameras capturing into the same render texture).

This is the setup below

Now, this works fine and all, as long as I have the secondary camera use a solid color instead of depth only AND give it a color that has an alpha big enough to show the semi transparent background on top of the current camear, but if I take the alpha down, or move back to depth only, then the particles don't get drawn at all.

It's as if the camera doesn't capture anything unless there's a background behind it.

The render texture seems to capture the alpha components correctly, regardless of background color, but the RawImage component will just ignore it. So even though I have the render texture that I want, I have no way of showing it correctly.

Any ideas?