Let's start off by giving a few references:
Milani, TL, & Hennig, EM (1993). Pressure distribution under the foot at the take off in volleyball jumps and high jumps Fosbury Flop. In Biomechanics XIV, (pp. 874-875). Paris: International Society of Biomechanics.
Energy absorption of different court surfaces: http://www.asbweb.org/conferences/1990s/1998/86/index.html
Volleybal Biomech Differences btw Sand and Rigid surfaces in Squat Jump: http://www.ncbi.nlm.nih.gov/pubmed/15079993
Orthotics do have an effect on the angular alignment of the bones of the foot in stance and it is widely accepted that these changes translate to a change in plantar pressures and center of progression during gait. The degree or magnitude of effect on pain and function is not well known and published results are largely subjective or speculative. Too bad. But what we do know is that by altering the plantar pressures during gait, we can elicit the effect of breaking a player's cycle of loading the foot in a painful area and relieving an overused area of compensation. But what about the playing surface and how can we reduce the risk of injury occurring in the first place??
In Jumping, the softer and more compliant a surface is, the greater amount of force is transferred to the jumping surface. Additionally, the body will make angular compensations at the LE joints and hips to improve stability, increase extension moments, and launch during a jump. It would appear that the softer surface (Sand) reduces the likely hood of impact injuries but at the expense of increased loading of the support structures of the foot and ankle at angles that do not occur on a more rigid surface. Compensations such as these are highly individualized and each player will have their own method of positioning themselves for proper launch and landing. This would be enhanced in barefoot conditions v. shod.
The lesson to take away here is that an orthotic can have very little effect on the alignment of the LE on a typical sand volleyball court. Depth of sand and a billion other assumptions are being made of course, but if a team is training on sand, they should schedule their matches for sand surfaces as the body will have learned to perform on that surface. A player may actually jump higher on rigid surfaces having trained on sand, but foot placement and impact forces will be dramatically different on the rigid court and an increase in the likelihood of injury may occur. Multi-surface training and an understanding of each individual's compensations to varying court surfaces are keys to injury reduction. An orthotic with good energy return, flex, support, and a shock-absorbing sockliner should help a player adjust to the changes in plantar pressures and bony alignments that are found going from sand to more rigid court surfaces.
Chris Gracey MPT, Cped