Nominally yes, but still has to adhere to EU rules which favour the owners of Capital not the workers. In the EU these are the norm, freedom of movement for employers, freedom of movement for workers and state aid. State Aid is the bit Corbyn seems to care the most about. Basically, the EU is considered an impediment to socialist government.
It also depends what you mean by socialism. If you mean Bolshevik Communism, then it absolutely is. If you mean Scandinavian-style social democracy, it is not. Corbynite Socialism is somewhere in between the two.
The EU is not an obstacle to national ownership of anything.
Part seven, article 345, of the general and final provisions of the Treaty on the Functioning of the European Union make that clear and it says "The treaties shall in no way prejudice the rules in member states governing the system of property ownership." The EU can't stop you taking the railways, say, or water, into public ownership. Nor can it stop a government becoming the majority shareholder in a car firm, BUT It can prevent the emergence of a monopoly, whether it is private or public. It ensures competition in provision. Public providers must be treated on an equal footing to private ones and any state subsidy must be available to all operators, whether private or public. There is an inherent contradiction there. Remember that a lot of subsidies go to multinational corporations.
The EU requirements force governments make their state aid payments transparent and demonstrate what type of behaviour they're intended to incentivise. In the last Labour manifesto it would have been difficult to establish the National Investment Bank and Regional state owned power companies, because of competitive tendering rules. That is a limit on national power.
In effect it is anti- socialist as EU free market rules prohibit national governments from planning economic development through regulating the movement of capital, goods, services and labour, across and even within the country’s boundaries.
Planned economies are, in effect, outlawed by Article 3 (for a ‘highly competitive market economy’) of the Treaty on European Union and by TFEU Articles 119, 120 and 127 which repeatedly demand that all EU member states operate ‘an open market economy with free competition’.
The EU Stability and Growth Pact sets limits on public sector financial deficits (3 per cent of GDP) and accumulated national debt (60 per cent of GDP) and commits member state governments to achieve balanced or surplus budgets.
EU directives have enshrined Value Added Tax as the EU’s ‘tax of choice’. Such indirect taxation favours the rich because everyone pays the same rate, whereas taxes on income or wealth can be levied at differential rates according to people’s ability to pay. VAT must be imposed in all member states at a minimum of 15 per cent on most goods and services (in Britain it is currently 20 per cent), or at a minimum of 5 per cent on specified essential items not already zero-rated. Only outside the EU would a British government be free to reduce or abolish VAT, not least as part of strategy to combat poverty and inequality.
The EU is also seen as being Imperialist, it looks after the Western free market economies at the expense of others. that has been debated on here at length.
This is a summation of the LEXIT view of the EU and not my personal view and was collated with the help of various websites as I wanted to try and cover it as best I could because the view is pretty much dismissed on here and it is highly relevant to any debate in my opinion as it helps explain why there is a split in the Labour Party between the Corbynites and the Blairites.