Scottish universities have certain positive obligations in law, but they are bit more abstract than this. It is not a matter of whether a university must fund dyslexia assessments in a specific way - the obligations are to the effect that when universities make and apply policy of any kind, they have to take the needs of disabled students into account. On this basis, suppose a university has a particular support system for students with dyslexia, which they decide to stop. That decision is not inherently unlawful, because the law only requires that the university have "due regard" to particular defined needs. They might have properly considered the effects but still decided to withdraw funding based on the overall context of their operations. Or they might not have considered them, which is a problem. But they are not positively obliged to run a particular programme; their statutory duty is at a higher level of abstraction.
These requirements are part of the "public sector equality duty" (PSED), which apply to Scottish universities as well as many other bodies. They are in addition to the general equality law on non-discrimination. Scottish universities also have so-called "specified duties" to periodically come up with "equality outcomes" and report on their progress towards them. The PSED does not only apply to disability, nor only to the education sector - it binds a wide variety of public bodies on several axes of potential discrimination.
You can learn more about the PSED from the Equality and Human Rights Commission, or by reading its definition in the Equality Act 2010 s.149. For a specific university, searching on the web for
[name of university] "equality outcomes", or similar, should show their statutory report about how they are trying to achieve the PSED requirements. In earlier years, there was an effort to produce a statutory code of practice for equality duties in the higher education sector (which might have included material about disability support services), but the current government has backed away from taking that forwards.
There are not many avenues for challenging university policy. Outwith the structures of the university itself, the only legal route is by petitioning for a judicial review in the Court of Session, which is a serious business. The expectation is that people who object to university policy should, in the first instance, address themselves to the university's governing body.
Beyond policy, a specific aggrieved student has other possible actions, because regardless of the university's general policy, they are still not allowed to discriminate against disabled people in specific ways. So, a student who has experienced hardship due to their dyslexia or dyspraxia has various courses to take, even if university policymaking is hard to challenge in itself. They can point to the discrimination they actually suffered.