touch enabled

Is a page with the dhtmlxgrid touch enabled on a tablet by OS default?

Unfortunately your issue is not clear.
dhtmlxgrid does not support the touch.
you may use the dhtmlxTouch functionality.

Sorry let me state it this way
Would a webpage with dhtmlxgrid on an OS that is touch enabled(Win7, Win8) on a tablet be also touch enabled?

dhtmlxgrid is not designed for the touch devices.
Please, try to check some online samples:

For touch devices you may try to use the dhtmlxTouch:
or the Webix datatable: