I wanted to know what I can do (if I need to do anything) to ensure that the plug-in works well with WP Email Template (+ Pro)?
Please download the Lite version and test - If you find any conflicts with your plugin please let me know - there are no known conflicts with any other plugin so I don't see why yours would be any different. If the Lite version is compatible the Pro version will also be the same.
Event Organiser Pro itself uses wp_mail(), but it also has its own template options - these essentially insert the body of the e-mail into one of a selection of pre-defined HTML templates.
That is exactly what WP Email Template does - apply a mobile responsive HTML template to all mail that passes through wp_mail()
If your user choose to apply the Templates You have built into your plugin - then WP Email Template will still apply the template and it won't look good - which is the same with any other plugin that applies it own custom HTML template and uses wp_mail()
If a user has WP Email Template installed - as long as you have in your options as setting "Don't apply HTML template' then there will be no conflict. They can just set up the template they want to apply to all email generated from their WordPress site and it will apply to your plugins emails - just as it applies to all emails. That is why WP Email template is popular amongst users - because it gives the site consistent branding - See this from the Plugins description
Why we built it
We built this plugin because we believe it is important that every contact we have with our clients carries our brand. We just hated those boring unbranded plain text emails WordPress generates and the unbranded html styling some plugins apply to our contact with our customers. So we built the WP Email Template to make sure that every contact our online customers have with us carries our brand. We have used it for a while now and just love it.
Thank you and All the best with your Pro-add-on release