Well, this question is ridiculous. So let me go through this (Because my OCD went off) :P
Can starters become HA? Better wording: Can starters' ability change to HA?
No, Pokemon cannot change their abilities. Pokemon can use their alternate non-hidden abilities via ability capsule.
Can Starters have a HA?
If it has been released: For example, the Alolan starters HA's were unavailable until a recent distribution via Pokemon bank. Other ways HA starters (or Pokemon in general) have been received are: events (like HA Torchic), breeding ones that already have HA, transferring most Pokemon from the GBA VGCs to Ultra Sun/Ultra Moon will result in them having an HA (works for all starters), Dream Radar, and Friend Safari (all Pokemon in Friend Safari have a chance to have an HA, and there are various starter Pokemon available in it).
