Yes
When you open your tiff that has and embedded sRGB color profile in Photoshop. It will open as a three channel document the is in SRGB Color space. If you use menu Image Mode Grayscale the document will be converted to s single channel Grayscale image and convert to a Dot Gain 20% profile.
Photoshop is a document editor not a file editor your Tiff file on disk is still a sRGB Color image. The document in Photoshop is not. When you save a file for the document the File will have A grayscale image Profile Dot Gain 20%. I added gray to the document name when I save that tiff file or PSD or PNG. Whatever you use in Save AS.
I use a newer Photoshop I no longer have CS3 installed. Photoshop has not changed in that area
