I think it depends on who owns the rights. Alamy enforces the copyright on images regardless of whether they are rights managed or not, and my own photos are sold mostly pretty cheaply as rights managed, while they place restrictions on royalty free, so I think the lines between the two are more blurred than perhaps they were at one time.

You can get sued for using any photo that you do not have the rights to use - regardless of what licence it's offered under.

The lesson here is to avoid any image that you do not have the right to use... or be prepared to face the consequences.