HTML in custom blocks: git and editor integration?

It's a complicated matter, because Drupal isn't keen on adding self-made HTML in his projects. But, however, you can force Drupal to use your HTML code by using the hook_block_info() and the hook_block_view() function. In this way, you will add a block in your code (you can easily access the code by using Eclipse, Aptana,... or any other editor your developers like).

Here is an example:

function yourmodule_block_info() {
    $blocks['blockname']['info'] = 'Some info about the block';
    $blocks['blockname']['cache'] = DRUPAL_CACHE_PER_USER;
    return $blocks
}

function yourmodule_block_view($delta) {
    if ('blockname' == $delta) {
        $block['subject'] = 'The subject of the block';
        $block['content'] = 'This is the content of the block';
        return $block;
    }
}

In this way, you can add just about anything you like in the $block['content'] part.

I hope this helps you out a bit. If not, please let me know!

Probably the simplest way to do blocks this way is via the Nodeblock module. As the developers describe it

This module allows you to specify content type(s) as being a block. This allows the content managers of the site to edit the block text and title without having to access the block administration page. Users only need edit access to that node in order to edit it.

Not only does this make it possible for users to edit blocks without having admin permissions, it also lets you do versioning and use the normal html workflow you would use for any node.