I'm wanting to add some Brettanomyces lambicus to an old ale after it has been moved to a secondary fermentor (it should be in the 7-8% ABV range at this point, and the primary yeast will be Wyeast 1968, if that matters). Do I need to make a starter for it, or can I just dump the culture directly into the beer, cap the fermentor, and let it go for the rest of the year?
Yes, I think you can just dump it right in, with no starter.
Warning: I suggest that you double your normal sanitizing procedures with everything that comes in contact with the Brett. A couple of years ago I added the dregs from a couple of bottles of Orval to a batch, and the Brett showed up in quite a few of my subsequent batches. I dumped out probably 15 gallons of beer due to this.