It depends on ORM Framework you're using. ORM Designer display for each ORM framework datatypes which are officially supported. You can also add new datatypes to configuration files manually, but it depends on ORM if they accept datatype defined like this.
For example if you would like to add new datatype to ORM Doctrine, edit file Doctrine.ormd2.cfg.xml. You can also override configuration by your own file. More here: http://www.orm-designer.com/article/ormd-developers-configuration-files-structure and add new type here:
<data-types>
<data-type name="boolean" />
<data-type name="float" />
....
</data-types>
But as I said before, it depends on ORM if new data type will be accepted.