Your guests will think it's fun, not tacky - people actually remember food truck weddings way more fondly than the standard rubber chicken dinner. The casual vibe makes folks feel less stiff and more willing to actually mingle instead of sitting at assigned tables the whole night. I'd be more worried about logistics than perception. Make sure you have a backup plan if weather turns nasty, enough serving stations so there's no huge line forming, and think about timing - you don't want a gap where people are standing around hungry waiting for the truck to finish setup.
Here's the thing nobody mentions: hire someone to plate and serve the food nicely even if it comes from a truck. Seriously. Get a couple people with catering experience to put the tacos or whatever on proper dishes, maybe add a garnish, and hand them to guests. It takes maybe $300-500 extra but makes the whole thing feel intentional instead of chaotic, and your photos look way better. Your guests still get the fun interactive element but it feels more elevated. Also double-check your venue's rules about trucks pulling in - some places have weird restrictions about where vehicles can park or how much notice they need.
The tacky concern is really about execution, not the concept itself. A well-organized taco bar with good signage, nice napkins, and a drink station nearby reads as thoughtful and budget-smart, not cheap. People these days genuinely prefer this kind of thing over formal sit-down anyway.