No! There is no scientific consensus that sufficiently low doses of ionising radiation are unsafe.
First, you have two different claims here.
- "Scientists agree that Linear No Threshold (LNT) is valid at all doses"
- "Scientists agree that Radiation Hormesis is wrong"
The Radiation Hormesis hypothesis states that low doses of ionising radiation can be beneficial, while a model where below a certain level ionising radiation simply has no discernible influence is something else.
But we can cut the Gordian Knot here by simply answering:
No, there is not consensus that LNT can be used to estimate an actual physical effect of ionising radiation at low dosages. The Wikipedia article you linked to describes the "controversy" about this. There are those that oppose using LNT as a tool for judging damage made by low dose radiation:
In conclusion, this report raises doubts on the validity of using LNT for evaluating the carcinogenic risk of low doses (< 100 mSv) and even more for very low doses (< 10 mSv). The LNT concept can be a useful pragmatic tool for assessing rules in radioprotection for doses above 10 mSv; however since it is not based on biological concepts of our current knowledge, it should not be used without precaution for assessing by extrapolation the risks associated with low and even more so, with very low doses (< 10 mSv), especially for benefit-risk assessments imposed on radiologists by the European directive 97-43.
In accordance with current knowledge of radiation health risks, the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 rem (50 mSv) in one year or a lifetime dose of 10 rem (100 mSv) above that received from natural sources. Doses from natural background radiation in the United States average about 0.3 rem (3 mSv) per year. A dose of 5 rem (50 mSv) will be accumulated in the first 17 years of life and about 25 rem (250 mSv) in a lifetime of 80 years. Estimation of health risk associated with radiation doses that are of similar magnitude as those received from natural sources should be strictly qualitative and encompass a range of hypothetical health outcomes, including the possibility of no adverse health effects at such low levels.
There is substantial and convincing scientific evidence for health risks at high dose. Below 10 rem or 100 mSv (which includes occupational and environmental exposures) risks of health effects are either too small to be observed or are non-existent.
No there is not consensus, there are those that claim LNT is valid for low doses, and those that say it is not.
This does not mean that there is consensus that Radiation Hormesis is correct either, but that is a separate discussion.
The reason there is this debate is because — once the radiation dose drops low enough — other carcinogenic factors glare out the effects of ionising radiation, and cause the latter to get lost in statistical noise. It is like trying to hear a whisper in a crowd when everyone else is shouting.
While we cannot say for certain that LNT reflects reality at low doses, it may still be used a tool for determining policy. But even in that role it is contested since determining policy after minuscule doses may cause radiophobia and/or unnecessary bureaucratic hassle, but that is another discussion.