Yes, dogs can get pregnant without tie or lock. Tie in dogs is part of mating but not necessary for pregnancy because sperms are released in to female immediately after penetration. Anyhow, tie in dogs can facilitate the conception. Tie in dogs can last for 2-30 minutes with an average of 15 minutes.
The deposition of sperm requires penetration. If the male dog cannot penetrate the vagina, there will be no chance of pregnancy. Tying up is where the male's penis becomes entrapped in the vagina after mating. This is normal, and can last from 20 mins to an hour. I do not know why this would not occur if both male and female are healthy, but it is not necessary for fertilisation.