I do this. Well, not as much as I did, but I have two accounts. AFAIK, it's fine.

Also top tip: no need for crazy scripts or anything else. (As long as you don't want different settings/keymaps on the other acct)

1) Copy your DDO directory to somewhere else
2) Have shortcuts to both launchers
3) Open launcher 1
4) Open launcher 2
5) Login & hit Play on both

You don't need any fancy timing or anything between 3) and 4). The DDO client only seems to do the check for other open instances once you've hit "Play", so you can open at your leisure as long as you leave all clients at the launcher whilst opening them up, then log in one by one.