This seems really unlikely to me. Assuming they're saying each letter and not wordifying it into a single weird syllable, it's actually more effort to say "eff tee ell tayp" than it is to say "va-kyum tayp". One of the main points of slang is to shorten something to make it easier and faster to say (cockney rhyming slang being one of the more obvious exceptions). Working class Brits say "loo" instead of "lavatory" because it's at least (depending how you pronounce the latter) two syllables shorter. In Australia, we say arvo instead of afternoon. In parts of Midwestern America, they say "spendy" instead of "expensive".

Slangs are a great way to add life in any fiction. As you illustrated with the GRR Martin's novel above, it shows the characters are aware of their environments and interacts with it.

A better slang might be something like "vac tape", 2 syllables instead of three and gets the point across unambiguously.

Or "Space tape", or even simply "Tape". just keep using "tape", and the readers will follow it.