@witslk,
Try this code then,
add_filter( 'bp_email_use_wp_mail', function() { return false; },99);
If it does not work then check with this code:
add_filter( 'bp_email_use_wp_mail', '__return_true ' );
This is a limitation of buddypress, it will only send emails in HTML if it detects that the wordpress mail filter is not altered.
This is buddyPress code and it does not proceed if it detects some plugin is using its own mailer function at wp_mail hook :
http://prntscr.com/k88jgj