If the requirement to ‘disable the possibility to hiding columns only for subset of all columns’ means that you would like to disable ‘Select Columns’ menu in WebGrid column action context menu, then you may simply set the value of ‘AllowSelectColumns’ property to ‘False’ in LayoutSettings tag.
*AllowSelectColumns property specifies whether or not to allow users select columns from within WebGrid.

...
<LayoutSettings AllowColumnMove="Yes" AllowGrouping="Yes" AllowSorting="Yes"
    AlternatingColors="false" ShowColumnAction="true" AllowSelectColumns="No"
</LayoutSettings>
...

If you wish to disable only specific column to be available in ‘Select Columns’ menu in WebGrid column action context menu, then please try to set the value of ‘ShowInSelectColumns’ property to ‘No’ in the WebGridColumn tag.
*ShowInSelectColumns specifies whether the column will be shown in Select Columns menu.

...
<ISWebGrid:WebGridColumn Caption="Name" DataMember="Name" Name="Name" Width="220px"
    ColumnType="ImageAndText" ShowInSelectColumns="No">
</ISWebGrid:WebGridColumn>
...

Please let us know if you have different scenario.