I do like the idea of ranking players through well balanced bots that can emulate different playing strengths. However, I do feel that currently there are few bots that can emulate weaker play strengths adequately. Making all bots able to deliver ranking points is particularly tricky since their weaknesses are often directly attached to their glitch factor.
AFAIK, ranked games against bots were always allowed, but they effectively didn’t count because all the bots were provisional until they completed an enormous number of games—on the order of 10,000 for Kugutsu, if memory serves. The number of required games differed from bot to bot (it was listed on each bot’s profile), which may tie in with @Adam3141’s comment above. Of course, games against provisional players become effective in the ranking after the account is no longer provisional (including bots). When Glicko came in, I saw a statement somewhere that this long provisional status for bots was eliminated (indeed, the number is no longer displayed on the bot profiles). Hence, bot games appear to be ranked and effective, presumably after the standard 5-game provisional status.