It depends on what type of problem your orthotics are trying to cure. People with flat feet (like my wife) usually get an orthotic with a minor arch built into them. The metatarsal bump that's been mentioned isn't used unless you have the specific forefoot issue that would benefit from it. If you have that need, then it would be a must for cycling, since the forefoot take most of the load.

I have worn orthotics for over 25 years due to some sort of problem, similar to plantar faciitis,that affects the tendon running through the arch. Even with a high arch, I never used or felt the need for orthotics in my cycling shoes. In fact, the only time my feet didn't bother me was when cycling, since the arch and heel see little involvement. In the last few years, I have invested in D2 custom cycling shoes that include a custom orthotic. They've worked quite well, but aren't any miracle and cost a lot. Prior to that, I used Sidi shoes than have a built-in arch support, rather than a flat insole.

One problem with cycling shoes is a lack of room for orthotics. Custom made orthotics for your walking shoes are not likely to fit into a cycling shoes, due to too much volume at the heel (mine don't). I've found a few brands that offer off-the-shelf thin orthotics that work in cycling shoes.

Another type of problem that many riders have never heard of is forefoot varus or valgus. If you have the more common varus, the foot tilts to the outside and put excessive pressure on the outside of the foot. I have the opposite problem, only on the left foot. You can buy Lemond wedges to correct the cleat angle and eliminate the excessive pressure. Some users of speedplay pedals blame the pedals for the uneven wear on the outside edge of the pedal, but the real culprit if forefoot varus. With valgus, the cleat spring wears a groove into the pedal spindle.