I find them incredibly helpful with substances like DMT and Salvia. They synergize very well. My theory is that things like DMT and Salvia have that dream-like quality to them. Like a waking dream. So if you are saturated with dream inducing plants or just combining the dosages together, DMT and something like Calea or Silene capensis, they do provide a sort of guiding force to the experience.
Salvia and Calea are especially good smoked together. The Calea has the effect of slowing the Salvia down a bit and making it more workable, extending the experience but also making it more manageable. Not on the same level as quidding but it can get very deep.
My changa blends almost always include oneirogenic herbs as I find they work well in concert with the harmalas to slow and enhance the experience.
When I work deeply with the Ubulawu herbs I find my DMT trips are greatly enhanced and the space is much more navigable. I do find my recall enhanced as well. Some of my best post-trip writings are from those experiences I've had while the dream herbs are in my system.
It's worth experimenting with
I would suggest working with the dream herbs on their own first, however. I think some people tend to underestimate the power of their dreams and how profound of an effect these herbs can have.