Waldron's first lecture raises a number of important issues, too many to be addressed in this posting which is why I wish merely to raise a query concerning this distinction. It appears to be based on taking the Kantian conception of dignity to reside primarily in a general picture of practical reason whilst the legal view of it that is raised by contrast is rather one that defines and describes a social standing and is hence not encoded in a general picture of practical reason. In response to this I want to raise a substantive point concerning the conception of right that Kant himself worked with.
Waldron's general concern in the first lecture concerns a certain kind of defence of "hate speech" legislation on the grounds that what is at issue in it is not an "intention" in the private sense on the part of the speaker but rather an effect that is at work amongst those to whom such "speech" (normally a form of writing) is addressed. The effect that is at work is one of reducing the respect shown certain members of minority groups such that they will not be taken to have a legitimate right to equal citizenship rights. As such this kind of "speech" undercuts the sense that there is a social contract to which all have a general kind of connection with. Since this is the point of the "hate speech" in question it aims to undercut "public order" not necessarily in the sense of wishing to instigate violence but rather in that it suggests that some are not truly within the bounds of the order that has been specified as public or not there in a full sense.
Waldron's general defence of "hate speech" legislation in these terms has much to commend it but does not fit well with his designation of the Kantian view of dignity as something generically distinct from the legal notion of dignity as a status and achievement. It is correct that Kant speaks of dignity in terms of his general picture of practical reason and in those terms it is presented as something of incomparable worth that we are all possessed of. However Kant's general picture of practical reason has to be related to his view of right. When we look at his view of right we find a conception of it that shows that there is Kantian precedent for the "legal" conception of dignity that Waldron speaks of.
In Kant's discussion of the preliminary concepts of the "metaphysics of morals" there is a definition of personhood that determines a person as someone whose actions can be imputed to them which leads on to the sense of a person as someone subject to no other laws than those they give to themselves (autonomy). This notion is important in connection with Kant's subsequent notion of right though it is far from equivalent to it. When Kant turns to specifying the notion of right it is done in relation to a "universal law of freedom" which involves coexistence of each freedom with every other (in the universal or supreme principle of right: Ak. 6: 230). Since this coexistence requires that right be founded on mutual restraint that is based on the ground of each person's freedom then it follows that for a legal order to exist is for the status of personhood to have been given form in such an order. Hence, legal order is itself a general achievement.
Kant's fuller account determines this order through notions of equality, freedom and independence (e.g. Ak 8: 290). It is true that the view of the last of these notions is problematic (and alters between the essay on theory and practice and the Metaphysics of Morals) but the notion of equality involved, as distinct from that of the freedom, is grounded in the order of the law whilst the freedom (which is recognised universally in human beings) is something that the law "restricts and realises". If we see the law as that which gives freedom its substantive content but also as something that requires equality in its nature then it follows that the Kantian view of legal dignity is one that matches the achievement sense given to it by Waldron.
The "hate crime" problem that arises from being based on the attempt to either reduce the scope of public status given to a member of a group or to find a way of expelling them from that status as such does thus violate the sense of equality of each before the law. In this respect then there is congruence between the Kantian notion of dignity and the legal sense given to it by Waldron. I won't here expand further on the question of "hate crime" though the nature of it (particularly in genocide) is something that is worth consideration in terms of its boundary and limit since it does present itself as one of the ways the social contract can be breached.