Using ImageOptimize plugin with Matrix fields
I'm also using ImageOptimize and yes, it does work within Matrix.
Your image has to have the call to the plugin code as specified in the plugin docs. Additionally, your image calls must match the image size you've setup within the plugin preferences panel. Within Matrix, you are calling the assets Field Type.

Here's a sample:

{% if block.type == "graphicCalloutBlock" %}
        {# Full Width Image #}  
        {% set image = block.graphicCalloutImage.one() %}
            &lt;div class="block"&gt;                               
                 {% if image | length %}
                 &lt;img alt=""
                 src="{{ image.optimizedImages.src() }}"
                 srcset="{{ image.optimizedImages.srcset() }}"
                 sizes="(min-width: 480px) 100vw, (min-width: 880px) 75vw, (min-width: 1024px) 50vw,  800px" 
                     /&gt;                               
                {% endif %}
            &lt;/div&gt;&lt;!-- end block --&gt;
{% endif %}