I always tell everybody, every watt of electricity you use is a watt of heat.
If the area where the watt of heat is added were 100% airtight, the fan would help for a bit to "distribute" the heat evenly around the hot box instead of letting it sit on one hot component. The battery is probably pretty hot in whatever spot the BMS is sitting inside of it, getting the heat off that spot faster would be helpful, but it's not going to help long term if the heat can't be vented out of the area. If the area has pretty good heat dissipation qualities (heatsinked walls of a nice heat transferring metal) it might help to distribute the heat to the walls and get it out of there.
I agree with the others, if it's not charging or pushing out huge loads while sitting in a hot box, it's probably not a big deal. Charging would certainly be the worst though, as wherever the watts of electricity "end their lifecycle", "get used", "converted to a chemical process", tends to be the place where most of their heat goes.
You can get large pieces of aluminum heatsink and attach those to the sides of the battery to help get the heat off the battery faster. It would work better for a metal cased battery than a plastic one, but even a plastic one it might help, especially if combined with a fan.
large heatsink example
The BMS is probably the real problem with the batteries in hot environments more so than the lifepo4 cells themselves, think about your phone/computers, etc.. they get pretty darn hot, and the BMS is similar but it's locked inside of a box with no airflow and strapped to lifepo4 cells with the dinkiest little metal plates or heatsinks on it.