No, MLB players on rehabs, like Gregerson’s will be, do not count against the 25-man minor league active roster.
Holland, on the other hand, was not injured. Therefore, a rehab was not available. He had to be optioned out just like any other player, using one of the 25 spots at Palm Beach.
Also a good reminder for me to make sure I am clear in my articles. It is easy to fall into the trap of making assumptions. Better to overexplain than underexplain.