Hello BladeForums, and Hillst1
As it happens, I have two of the guyots, and the vargo mug - carry & use them regularly.
Yes, the Guyot (I'll speculate you are referring to the 38 oz) stainless steel bottle does nest in
the Vargo titanium Ti-lite mug. In fact, there's just a tiny bit of "wiggle" room left over.
A regular 32 oz nalgene will also nest in the cup, as will the taller 48 oz "Silo" nalgene.
Though I don't own the SnowPeak mug, I've handled "a few", and they do not seem noticeably different
in thickness, or "smoothness". I say smoothness because, the Vargo and SnowPeak are finished very smooth.
Not all titanium mugs are though, if compared.
uw