Is it a sign of progress when the pigs are seen walking on two legs in Chapter 10 of Animal Farm?

It is definitely not a sign of progress that the pigs walk on two legs as the pig has symbolically become man. That is, this action of standing upright signifies regression to the behaviors of the oppressive human who has been overthrown in the revolution.

In the beginning of the narrative when Old Major speaks before the animals, he tells them that Man is "the only real enemy we have," urging them to rebel against their slavery to the farmer, Mr. Jones. Old Major insists that “whoever goes on two legs is our enemy." He further declares, “all animals are equal,” and orders them to not exhibit any behaviors singular to man.

At first, the pigs assume the supervisory role as they are the most intelligent of the animals. However, the fact that power corrupts is evinced in Napoleon, who sabotages Snowball's innovative ideas and destroys the windmill he has engineered. Napoleon, then, becomes the sole leader and appoints Squealer as his "press secretary" to spin what has actually occurred so that the animals will accept things as progress. Little by little, the ten commandments are eroded because the other animals cannot read and Squealer convinces them that their memories are in error. Also, the weaker animals are terrorized into submission. Thus, Napoleon becomes more and more despotic until he is seen in the farmer's house drinking alcohol. Then, in Chapter 9 Clover calls to the other animals to witness what she has seen. "It was a pig walking on his hind legs. Yes, it was Squealer."

In the final chapter (10), the corruptive nature of power is exhibited as the pigs are seen with the humans, who have congratulated these pigs on the long working hours and low rations imposed upon the lower animals. Men and pigs all stand together, the pigs indistinguishable from the humans. Clearly, the standing pigs symbolize their absolute corruption.