Can uniques or mythics still come from obol gambling?

Uniques can still show up from obol spending, but it is rare enough that a lot of people go a long time without seeing one. Mythic drops are a different story and seem way less likely, to the point that most players treat them as basically off the table from that source.

The load screen message may be technically old or at least misleading in how much hope it gives. If you are trying to target specific gear, obols are still useful for volume, but not something I would count on for chase items.

The short version is that the system can still spit out uniques, but it is so inconsistent that plenty of players think it is bugged or removed. For mythics, I would assume the answer is effectively no unless the game changes or someone gets an absurdly lucky result.

If the goal is just to improve odds on a unique for a certain slot, obols are still one of the easier ways to roll that slot repeatedly. If the goal is mythics, farming content with actual higher-end drop tables makes a lot more sense than gambling obols.

I would not trust the loading tip as proof that the system is current. Game tips get stale all the time, and this sounds like one of those cases where the text survived longer than the real usefulness of the mechanic.

From a player standpoint, the useful takeaway is simple. Spend obols if you want a shot at rares and the occasional unique, but do not build expectations around mythics. If you see one, it is a lucky outlier, not the norm.