TBDs are a pretty common issue with greyhounds b/c they spend much of their life in the South - usually by the time the dog goes to adoption they're already in the subclinical phase and show no symptoms. Then one day the dog can become extremely ill seemingly "out of the blue" - Since greyhounds usually race in one state and are shipped to many other parts of the country, there is a problem with vets in areas that don't have high incidences of TBDs overlooking the diagnosis and resulting in delayed treatment or even death of the dog.
That said, I have a few dogs that have/had Ehrlichia. Specifically a father and two of his offspring (a track well known for having dogs with tick disease...but that's another rant altogether). A titer will show you exposure, but won't necessarily indicate whether or not a dog needs treatment. Most vets would want to see clinical signs along with a positive titer. Also keep in mind that even after treatment your dog may show a positive titer simply because they were once exposed to the disease.
TBDs are really a very tricky thing. There is much debate in the greyhound world about how to treat, when to treat, whether or not to treat proactively (i.e. a dog with a low positive titer but no symptoms).
There is a SNAP 4DX test that your vet can use in-house to look for heartworm and three tick diseases. For a more definitive test, though, I'd have blood sent to NC State for a tick panel (which I would do only in the case of a sick dog). Your vet may or may not stock the SNAP 4DX. In a non-endemic state, I would imagine not.
Here's a pretty good article written by a vet I really respect:
http://greythealth.com/ehrlichia.htm It's heavily focused around greyhounds, but the info could apply to any dog.
I think the most important thing is to educate yourself on the symptoms of tick disease so if your dog does ever become symptomatic, you can advocate on behalf of your dog if your vet happens to be one of those who considers everything BUT tick disease.
Tick disease is not something I test any of my dogs for on a regular basis...certainly not yearly.