Many people expect their voice teachers to be both without realizing this is not always the case. A GREAT instinct is to find someone who can sing in the style you wish to sing as well. These people know which sounds, vocal effects, etc. are best for the style. However, this does not qualify someone as a vocal technician. The teacher may be great at utilizing his/her voice, but (s)he does not know the ins and outs of proper voice function.
I had a student once who studied with me until she went to college. She and her mom told me that after lessons with her previous teacher, she could not sing or speak! That is HORRIBLE teaching! "Sing like me" is not enough for most people! My student said she basically just screamed in her lessons until she couldn't sing anymore! She didn't know better; she just did what her teacher told her to do! She made the sounds but not healthily! Why did she do this? Because her teacher was an amazing singer for the style! After our first lessons together, she left with the biggest smile on her face because her voice didn't hurt, and I helped her progress in her talent!
Vocal technicians are those who have studied voice to the point of easily identifying vocal faults and helping you solve any/all problems that arise while you sing. Again, they are not guaranteed to simultaneously be a coach for your particular style! As great as they can be at working with you, they may not always know how to help you with your style of music!
The best teachers are those who can be both for you! Mostly because of less time and money since you don't have to travel between two people.