Vanilla is an orchid, or in the orchid family, (I think). And it's probably the host trees in stress conditions that attract the ants, not necessarily the vanilla plants themselves. So, planting companion plants, or putting out bits of dried herb is going to be quite an undertaking, especially in the tropics.
Henry mentioned that the ants are colonizing or attracted to the pruning cuts on the host trees. If you could increase the soil health and the health of the trees, maybe making pruning cuts during the proper moon cycles, etc., you'd begin to see some differences. Peter mentioned asking the ants to leave. Interestingly enough, I read one book on 'talking to animals' (From the Horse's Mouth), kinda humorous treatment of the subject. But she said ants are among the more suggestive in the animal kingdom as they follow a signal trail left by their navigator/leaders. It's fairly easy to dissuade these trailblazers to go elsewhere and leave your things alone. I've had some moderate success with this in my kitchen with fire ants, a particularly belligerant type. You need to disrupt their pattern (stir around in their orderly marches) to get their attention, then address yourself to the ones laying the trail (they're usually larger than the worker ants). Often they'll move over, and you have to explain that you want them to abandon the entire project (of your cabinet or countertop) before they understand. Sometimes it takes mashing one or two of the leaders before the workers get the 'bigger picture'. I have one blue and gold macaw in the kitchen who is constantly dropping food bits to the bottom of her cage. I'm lucky if I take up papers and scrub out the cage floor a few times per week, so often, especially in warmer months, she can create a fly / maggot problem. (ugh is right!) but the fire ants generously keep her cage spotless for me. Once they climb the bars and start peeking in her food dishes, I move them on out, but otherwise, I've found that working with ants is easier than I thought.
