I mostly ride dirt & gravel roads up here in Canada (they're so quiet!) so I took great interest in the Eroica this past two years. I can't remember brand names but a couple of the reports stated that they used nothing special for tires - 23 and 25mm stuff. After all, they only do 57k on dirt out of an 190k race.
I use a cyclocross bike on my dirt roads and last year used Challenge Grifo XS tires which are 32mm wide. They're expensive but oh so plush.
I sometimes go riding on fire roads and some single track here in Northern California and I just use regular tires. Ya, the mountain bikers look at me like I'm crazy and ya I slide around a little bit, but it's fun. Right now I have conti gp 4000s, but I've ridden all kinds of 22 or 23c tires over the years and they all work fine.
Probably any kind of 25mm tubular tire will do just fine. Conti has the Competition in 25mm even with an extra protection layer. The Vittoria are nice tires too, I think they also come in 27mm and then there are Schwalbes Stelvio in 25mm and probably some more... I have driven Stelvio 23 over the worst gravel roads and they did a very good job without flattening.
My stomping grounds are luckily abundant with hard pack dirt, so I can get away with a 23mm Michilen Krylion carbon, for under 100 clams. The more loose or soft your surface, the wider tire with some tread would be better. In the past I've fit 27mm Conti Top Touring on my Colnago MasterXLight. Most carbon race bikes these days will accept 25's, that's good enough. Now get out there and ride the Vitamin G!!!!