On the occasion that dappled lighting dominates a ceremony site, options are few and far between for adequately lighting the scene. Flashes can be used if discreetly placed, but even then, they might not be powerful enough or space may be too limited to place them out of sight. If this happens, highlights and shadows can be adjusted in post, and HDR presets may bring about usable clarity, but there is only so much that can be done.
The best way to approach such a scene is to discuss the ceremony site and time of day during the talk through, hopefully early enough in the planning process to make changes. If the potential psycho lighting nightmare is addressed early on, the situation may be avoided, or at least the bride and groom will know what to expect for wider shots of the site.