Are any of the current autorig component presets suitable for surface constraints? I'd like to do something akin to the KineFX example where I snap the non-dominant wrist to the closest point on a quarterstaff.

See example "Example 2: Attaching a teapot primitive to the nearest primitive on Flip’s surface" here:

https://www.sidefx.com/docs/houdini/character/kinefx/constraints.html#surface-constraint [www.sidefx.com]

No but if you do your own component, you can make use of rig::PrimConstraint and/or rig::UVConstraint.