Tokudb storage engine as mysql-cluster storage engine
I think you are mixing concepts here: Mysql Cluster (assuming you are referring to MySQL NDB Cluster) requires the NDB engine for tables that are part of the cluster. In other words, NDB is the cluster, and MySQL Server, on the SQL layer, requires to use the NDB Cluster storage engine in order to access the data on the cluster.

TokuDB is an on-disk compressed format for MySQL optimized for large datasets. While you may be (or maybe not) able to install this engine in the MySQL NDB Cluster server distribution and use it locally to the node, it will never be able to be used as part of the distributed data, as that requires NDB.

There seems to be support of TokuDB by Galera in MariaDB Cluster 10, providing HA to TokuDB, but not the automatic sharding that NDB provides. I have not tested it, though.

Edit: Tim has told me on the comments that TokuDB is not supported by the Galera protocol in MariaDB (or at least not yet), only MyISAM (partially) and InnoDB, so not an option currently. So probably the only option for HA and TokuDB nowadays is traditional replication.