Dogs fr. HCM to Cambodia and back via land travel?

You better check with the bus company. There are such and such. I have seen living piglets and chickens transported, why not dogs to?  From some companies, I am sure, they will allow dogs (mostly Vietnamese companies).
If I would be you, I would search just after the border gate someone local, to do the dead. There are plenty of restaurants on each side of the boarder, where you can meet easy.

yeah, I saw these transactions before the border everytime I go to Cambodia, Thank you so much for the reply, highly appreciated.

You should contact to Travel company ( Viet travel, Saigon tourist). They will give you some information about carry pets. They are pro about the tour to Cambodia. I hope you can find the information  you want.
Have a nice day

This is just an update,  for months I've done my research on how to take my 2 dogs to Cambodia, good thing I did all those because I have shared information for exporting my beloved pet out of Vietnam. 

The sad part for me was that I was forced to buy a dog kennel of International Standard which is 2,200,000 vnd for my two dogs, they have both their kennels (1,100,000 each).   Had them vaccinated for their 2nd anti rabies vaccine although it is quite early but to avoid any prob.(poor babies of mine)

Different Vets tried to fool me of paying almost 3 million to 5 million vnd per dog due to different excuse like microchip, blood test to be send away on a lab. out of the country the other vet said hers is in Japan the other one is in Uk, Health Permit from the Government, and another paper, well to make it short they try to convince me that all are needed just to be sure that my two dogs can travel with me out of Vietnam.

I traveled via land to Cambodia (Phnom Penh). We tried the bus, If your dog is small enough like a chihuahua they can let you in, but since my two dogs are corgi breed, they are not allowed, they are on the middle size breed.  So we are forced to hire a mini bus/van from the Sorya bus company they charge us (5 people + 2 dogs) 100$, usually they charge more than that.  On the Border, both border no one as in "NO ONE" even cares that I carry a dog, no one ask for anything like papers, health certificate, dog booklet(their passport) I even ask if they are going to check my two dogs but they just said no, go. 

So to make it short, if you are going to Cambodia, its ok to take your pets even without certificate. or anything,  but it is always good to play safe.  so do be sure to have your dog booklet with you (books with the list of vaccines and stickers and sign of your vet) this serves as their passport,  vaccinate them with anti rabies, and the health permit which is very cheap (50,000 vnd only) from the Department of Animal Health. 

Hope this help anyone who have intention of coming to Cambodia with their pets. 

Great thanks for the information.