Can a vegetarian drink aloe juice to avoid B12 deficiency?
Aloe has not been identified as a source of B12. I have heard that consuming aloe vera alongside sources of B12 improves absorption of B12 and vitamin C. This article summarises the findings of a study that found this to be the case.
The claims in the article should perhaps be viewed with scepticism since the study was supported by a trade organisation for aloe vera products. More importantly, the fact that aloe vera is only thought to improve absorption of B12, not to provide it, tells you the answer to your question - that aloe itself is not a source of B12, and consuming it will not be sufficient to meet anyone's need for B12.
Lacto-vegetarians may obtain some B12 from dairy products. This question may be helpful.