"We do have examples of vampires being affected by religious symbols that are not their own"

I agree; but more convincing than your two examples (since they'd be recognized as familiar religious symbols, albeit from other belief systems) is the way Nick reacted to the obsidian knife in "Blackwing", since the episode doesn't suggest he's familiar with its religious role. It suggests that other people's beliefs can imbue a symbol with power to hurt vampires.

Not my favourite aspect of the multi-dimensional "what is a vampire?" question; but I know the spiritual/religious thing is popular with many fans.