This snippet will disable WooCommerce core emails based on the product category

functions.php

<?php

// Add the below to the bottom of your theme's functions.php:

add_filter( 'woocommerce_email_enabled_customer_processing_order', 'disable_emails_for_fundraising', 10, 2 );
add_filter( 'woocommerce_email_enabled_customer_completed_order',  'disable_emails_for_fundraising', 10, 2 );

function disable_emails_for_fundraising( $enabled, $order ) {

	if ( isset( $order ) && count( $order->get_items() ) > 0 ) {

		foreach( $order->get_items() as $item ) {

			if ( 'line_item' == $item['type'] ) {

				$product = $order->get_product_from_item( $item );
				foreach ( array( 'fundraising', 'cat2' ) as $category ) {
					if ( has_term( $category, 'product_cat', $product->get_post_data() ) ) {
						return false;
					}
				}
			}
		}
	}

	return $enabled;
}

Thanks for this. It works great :-)