[Vetrivel]

Try this:
{include file="customer/fts_featured_products.tpl" group="`$current_category.category`"|replace:' ':'_'}

or else
assign the value to the variable and then use it in the include
like this:

{assign var="catname" value="`$current_category.category`"|replace:' ':'_'}
{include file="customer/fts_featured_products.tpl" group="`$catname`"}