Yes, Ford Fusion Hybrids make excellent vehicles for flat towing. They've been approved/supported by Ford for flat towing for several years (since they came out basically), and have a great proven track record for such.
We have a 2013 Ford Fusion hybrid, and have been flat towing it since day 1, its been great for that. 'Tis really nice to have when camping, its ability to run silently and emission free on batteries is really nice to have at campgrounds. Its like having your own big, comfortable golf cart, haha. :)
I haven't read that much specific information on the 2014 models, but I can't imagine they'd be any different as far as flat towing goes. They're still using the same CVT transmission in them, so flat towing should not be any different.
As for the cost of the batteries if they need replacing after 8 years or 100,000 miles: If that happened, yes, it might negate some of the $$ saved in fuel mileage. However, how many actually keep a car that long? Anyone that does knows that when a car gets that many miles and 'age' on it, expensive repairs are something you just have to deal with from time to time. When the vehicle gets that old, a couple thousand for a new set of batteries is still a lot cheaper than buying another vehicle.
Also, as I recall, Ford actually rates the new Lithium Ion batteries to last 150,000 miles, so there is a really good chance you'll get a LOT more than 8 years or 100,000 miles before they need replacing. They may well last about the same as it'd be in a conventional vehicle before equally expensive repairs would be needed.
afrescop is exactly right, too - These vehicles are one of the easiest and most simple (of all automatic tranny 2WD vehicles) to tow. No pulling fuses or disconnecting battery, no need to start and run the vehicle every few hours to keep the tranny lubbed, no expensive modifications like lube pump or driveshaft disconnect needed, none of that nonsense. Just hitch it up, put it in neutral and go. Install a charge line like afrescop said (which is VERY easy and simple to do), and you can tow it all day, all night, all you want, and never have to worry about it.
Hehe, for us, one more nice thing about owning a hybrid: Where I work, to encourage folks to be more 'green', they just set up a bunch of reserved parking spots up front in the parking garage strictly for 'greener' vehicles that are considered LEFEV (low emission fuel efficient vehicles). Yep, the Fusion hybrid qualifies, they gave me a sticker for such, so I can park in the reserved spots up front. :)
We actually did not buy this car for its incredible mileage. We got it, spent the extra $$ for a hybrid, mostly because of how much simpler and eaiser it is for 4 down towing than anything else we looked at. That alone, for us, made it worth it. The mileage is just an added (very nice) bonus. That, and its just really cool having a vehicle that can run completely quiet and emission free so much of the time.
I see you live in Vermont. One thing I will caution you about, that the dealer may or may not tell you: Hybrid drivetrains do not do as well on mileage when its very cold out. There is no electrically powered heat, so when you turn on the heat inside, the gas engine is forced to come on more and burn more fuel to generate the heat for you (can't run in EV mode quite as much). Also, batteries generally are not able to store, provide power as well when its really cold, so gas engine has to do a little more of the work than electric motor does when its cold. Add that to the fact that colder air is more dense resulting in more wind/aerodynamic resistance at highway speeds...Well, in our case I've found that where I normally get about 48-50 mpg average when its warmer, now that its down to about 30 degrees here, I'm getting more like 45 mpg (how terrible, I know, hahaha).
