This is correct. The SDK's video modes only allow RGB output when using a PAL mode; however, PAL60 is basically equivalent to "NTSC", so using a PAL60 mode (aka EuRGB60) should work with RGB cables.
Sidenote: I keep seeing this misinformation that a red screen means your TV doesn't support NTSC. This is wrong; it means the Wii is set to an "NTSC" mode when you have an RGB cable connected, but it has nothing to do with the actual NTSC vs. PAL signal, since RGB doesn't use either of those encodings. The fact that Wii doesn't support RGB when using an NTSC mode is an entirely artificial limitation by Nintendo.