So I work in marketing and have suggested ads on Reddit for a few campaigns in the past. We were very much on the fence (and ultimately decided against) specifically because Redditors can be very ad adverse. This might honestly be enough to tip the scale and get them to allocate the money elsewhere. Why spend where it might hurt instead of help.

Sure but the messages might just be enough for them to decide Reddit is no longer profitable enough.

Don't think it as boycoting these companies, cause that wouldn't work.
But all it takes is one look at the news (on a very sad example, how target removed pride merch from their stores) to see it only takes a few loud voices complaining for some companies to shit themselves and adress the complaints. Right now, many of them are advertising in a protest / NSFW filled landscape... they may not take a liking to that.

Apple, a multi-trillion dollar company, when a few hundred redditors stop using their products for a week:

Not with that attitude! :D