RocksDB has a patent infringement license in it from Facebook. The legal team is therefore not comfortable with using it. For details read: https://github.com/facebook/rocksdb/blob/master/PATENTS
The alternatives include
1. LevelDB (https://github.com/google/leveldb) with a go wrapper (https://github.com/jmhodges/levigo),
2. goleveldb (https://github.com/syndtr/goleveldb) - a porting of leveldb in golang
3. BoltDB (https://github.com/boltdb/bolt)
BoltDB is suitable for read heavy workloads (e.g., LDAP) but has a relatively poor performance for read-write workloads.
Of the other two options, goleveldb is chosen because it is implemented in golang and hence easy to intergate and maintain.
In addition, as a precedent, ethereum go implementation also uses this package (https://github.com/ethereum/go-ethereum/blob/master/ethdb/database.go)