I think we should allow the link to the homebrew specifically, but not the link to the site's homepage currently in the question because it's not necessary. We should also quote or describe some of the homebrew to identify it when the page inevitably goes dead.
That's a weird conclusion but I base this conclusion on a few factors.
Let's get the most fundamental issue out of the way: do we accept the question? It isn't doing anything wrong itself, it's just asking about a piece of homebrew, so yes we should. That leaves the matter of how to clearly identify and reference the homebrew involved.
To identify it, we need to describe it or quote it. I believe our standard we'd expect from any new question would be to quote part of the homebrew and direct us to it, otherwise we'd close it as unclear, so we should follow that same standard here. Either way that means directing people back to the source, which is that page on that site that contains pirated materials.
Now, our policy about linking to dndtools.eu and similar sites was about proliferating references to piracy sites. It especially came up in the context of people linking to non-SRD materials (because they couldn't find it on SRD sites or on D&D Beyond) which represented an ethical and pragmatic problem: the ethical problem was we're effectively condoning piracy by hosting those references, the pragmatic problem was the site would inevitably become a 404 due to DMCA notices or other takedown actions.
Let's examine our situation against those two issues if we link back to the homebrew:
- The ethical issue: Here we aren't facilitating piracy. We might send a tiny bit of attention to the host site by linking to it, but the more we try to avoid naming it the more attention we'd also draw to it by our conspicuous reticence to reference the source properly. Would anyone know it even had pirated content if we didn't make a point of banging on about it? The more we say about why we're not referencing it, the more we're saying “hey, here's a great piracy source”.
- The pragmatic issue: it's going to 404 one day, so we should still describe the homebrew content so it can be at least somewhat identified. (It may get closed one day after the link dies.)
That leaves us with: describe (possibly partly quote) the homebrew and direct back to it like we would expect with any homebrew request, but do nothing more than that. Avoid drawing attention back to the site itself.
Usage of the site as a reference should otherwise be handled like normal: don't do that, and don't link to its non-SRD pirated content.