It's impossible to answer this. There haven't been any studies done on this.
However, I wouldn't try it, for a number of reasons.
First, if you are having an outbreak, virus could be shedding from areas of skin not covered by the condom. Acyclovir cream hasn't been studied for it's effectiveness in reducing shedding.
Second, condoms break, fall off - they fail.
Thirdly, what if your partner is allergic to the acyclovir cream?
Fourth, having sex during an outbreak, even if the outbreak is covered by a condom, can make the ob irritated, infected, etc. It's an open wound. Other bacteria and germs, including other STDs, can easily enter this way.
To be blunt, no one ever died from not having sex. You can wait until your OB is healed. There are lots of other activities you can do sexually that won't put your partner at risk. Pleasure them. Use hands - clean hands preferably protected by latex so bacteria doesn't enter the OB, depending on where it is.
Also on top of that, rubbing acyclovir cream on the whole area.