Is there a VEX function to obtain the value of an attribute at a specific frame?

any of ch() functions (like ch(), chi(), chf(), chs(), …) can take time as a second argument
so to get equivalent to chf() hscipt, just convert your frames to seconds and use as that second time argument

Hangs head, heads to help docs…thanks Tomas.

RTFM is always a great idea.