Is it safe to use stool softeners regularly?

Yes. It is common to use colace (docusate sodium) or docusate long term, especially when taking narcotics.
Yes. Stool softeners are safe to use regularly. However, i suggest that people add a fiber supplement and increase water intake first. Laxatives are another thing entirely, and should not be used regularly without a doctor's direction. This can lead to dependence of the colon on the laxative, which is not reversible.