As noted above, domo arigato is used from an “inferior” to a superior," which will include subordinates to bosses.
Perhaps in 17th century Japan, it would have been true for wives to husbands to use this expression with their husbands but this is 400 years later.
There are sounds which are dropped in Japanese, such as the final “u” sound in “des,u” but I’m suspecting that the posters here are not hearing the “o” in this combination. One reason is that the domo is acutally doomo, with the first vowel sound long. When “domo” is said by itself, then Japanese tend to shorten the sound. However, when used with “arigato” the situation is more formal, by definition, and hence an additional emphasis on the initial “o.” Non-natives not used to this would likely mishear this.