It's a complex topic, but in general any chemical treatment that kills slugs, snails or insects will be bad for hedgehogs and should be avoided.
The jury is still out on the effects that slug pellets have on hedgehogs. Metaldehyde is the active ingredient in most commercial slug pellets and research shows that the amount a hedgehog would need to consume to be lethal would be a very large amount either directly from eating slug pellets or poisoned slugs. However, there have been a few cases of dead hedgehogs being found to have had very high levels of metaldehyde in their system. There is also some concern, partly due to research on rats, that although the slug pellets may not kill hedgehogs they might affect their reproductive ability, having a negative effect on their population.
Less hedgehog food = fewer hedgehogs.
All things considered, to be truely hedgehog-friendly you need to stop using slug pellets or pesticides