I regularly do so with my own software. Only works for domains that other big dropcatchers are not after. It's easier and faster than trying to manually hand reg a dropping domain.
Namesilo has an API specifically for the sole purpose of dropcatching domains, which is only available during the "drop" time of day. You can use other registrars' api as well.
There is a limit on how many requests can be made simultaneously. Usually there is a 10 minute ban from the API if you go over the limit. It's different for each registrar, though.
For instance, dynadot does not limit you to how many requests per second, but you cannot send another request before the previous request has been processed.
Do note, that to register names via API, you must already have enough credit on your registrar account to cover the cost of registration ..