Yes, the Firebat's attack deals damage twice, although there is no indication of it aside from noticing the effect while in the process of playing or testing the map. The only other ways to know this are if someone told you or if you use an editor which displays it, which SCM Draft 2 does not.
It is unfortunate that there is not some method of determining this inside the editor, the only way is by saving the map and then checking it in-game, or looking it up. It would be much more convenient if there was an indicator that the unit attacked twice with each attack performed, perhaps this would be something to include in the list of suggestions for future updates to SCM Draft 2.
Aside from the Firebat, I know other units which shares this property are the Zealot, Goliath, and Scout. I'm not sure if there are others, as it has been some time since I've had to deal with this, but it is something you should certainly notice quickly when testing a map. Whenever you do notice a unit is dealing twice as much damage as you wanted them to, you will know that they exhibit this property and can simply halve their damage value.
Also, as previously mentioned, this makes armor twice as effective against a unit which exhibits this property. The reason for this is that the armor affects every attack twice due to the attack being delivered as two separate attacks (not that the armor is literally twice as effective against any individual attack). This being the case, a unit which attacks twice per attack will suffer a decrease in damage that is equivalent to double the attacked unit's armor value.
I hope that this answer has helped you further understand the issue that you've run into. If you have any further questions on anything or run into any other problems, make sure to let us know. Good luck with your current project, hopefully the rest of it goes smoothly.
Edit: Why would you report my post? I have answered her question as thoroughly and legitimately as possible. I covered all possible questions she may have on the subject, explained how it affects armor, and noted the only other units I know of which exhibit the same property. If anything, every other post in this thread should be deleted, since I've managed to answer the question better than everyone else combined, and included additional helpful information on top of that.
Edit #2: Vrael has erroneously suggested in the shoutbox that it does, in fact, tell you how many hits a unit has in the editor. Here is what the unit stats look like inside the editor.
The reason you do not see any indication of "max hits" is because it is not listed anywhere in the editor, as stated earlier. Please do not spread misinformation to new mapmakers if you're unsure of what you're talking about.
Edit #3: Apparently a number of people think it's cool to report this for being a serious reply to a "joke topic." The fact is, it only sounds like a stupid issue to you if you've been mapping for a long time. People with little melee experience and little mapmaking experience would naturally be stumped by why their unit is dealing double damage.
Post has been edited 7 time(s), last time on Oct 6 2010, 3:25 am by Azrael.Wrath.