Ciao all-
Roma-types are traditionally used, that's true. Mostly because they're fairly dry to begin with and they have a small diameter, so they work very well sliced lengthwise. I also dry cherries for trail snacks. They dry chewier, not as tomato-pasty as the larger ones, but sprinkle a bit of Italian seasoning on them and they're very nice little snacks. I always have a boatload of cherries and this is a way for me to cope with them all. So-called "traditional" Italian varieties that have worked well for me in my dehydrator are:
King Humbert
San Marzano (any strain)
Principe Borghese
Borgo Cellano
Black Plum - a Russian, but perfect size for this and makes a rich, almost smoky end-product
Any dry paste tomato should work very well. You want to stay away from the larger-fruited ones like Opalka. They're really too large to dry practically. You should micro-manage that dehydrator and take them out as soon as they lose moisture or they'll get black and crispy. You can still use them, but they'll have a decidedly burnt flavour, maybe not what you're aiming for. Start a small batch and work up. That way, if you mess up, it won't be a disaster.