Is it the same sausage as sai krok Isan?
No. Sai ua is a northern sausage grilled with herbs. Sai krok Isan is an Isan dish made by fermenting pork and rice, and its character is the tang that comes from fermentation.
Sai Ua · ไส้อั่ว
If you want a fragrant meat dish in Chiang Mai, choose sai ua. It is a northern sausage of pork mixed with chilli and herbs and then grilled. One slice gives you the richness of grilled meat and the aroma of herbs together. With sticky rice and vegetables it makes a good northern Thai meal.

The richness of pork is joined by the aroma of herbs and chilli seasoning. Its character is an aroma different from the sausages you know. The heat varies with the recipe, so if it is your first time, you can start with a small piece.
It is a sausage of pork mixed with herbs and grilled.
Sai ua often appears on the table of Lanna in the north. It is sometimes eaten with sticky rice or with a dipping sauce such as nam prik. Ordered with nam prik ong, which is flavoured with tomato, and vegetables, you can alternate between the grilled meat and the sauce.
No. Sai ua is a northern sausage grilled with herbs. Sai krok Isan is an Isan dish made by fermenting pork and rice, and its character is the tang that comes from fermentation.
The standard sai ua is made with pork. If you do not eat pork, it is better to choose another dish for your meal.
If you want to read more about these dishes and regions, these sources are a good place to start. Ingredients and cooking methods can differ from one eatery to another.
Sharing image credit: Takeaway · CC BY-SA 3.0