Jacqui,
It's been a few years since I did a NPLQ, but from my recollection it did not cover the syllabus of the First AID at work qualification. for example, Burns, Anaphylaxia and many other parts of the syllabus. It did cover CPR, Rescue breathing (as it used to be), shock among others specific to the Pool environment. For example far more in depth on Spinal injury management and patient handling, not seen in the FAW qualifications but important in the pool environment.
Therefore in my opinion I don't believe NPLQ would be an equivalent to FAW. With regard to appointed person / emergency aid, I think this may be acceptable to substitute AP with NPLQ. Best to check with RLSS for the latest syllabus and then cross reference against the HSE guidance / syllabus. Personally I would be looking for both NPLQ and FAW spread across various team members. For me they are two separate roles.
One final thought can you remove a lifeguard from poolside to commit to a first aid incident and maintain water safety? Probably not without evacuating the pool first and delaying your first aid response, unless you have suitable spare resource.

Jacqui - no I don't think that it does and we have both HSE FAW trained first aiders and NPLQ.

I should add that there is NO requirement for an appointed person to have ANY first aid training. Many providers used to include some basic first aid training for appointed persons BUT there is NO requirement to do so.

http://www.hse.gov.uk/firstaid/faqs.htm

I suppose the point that we may all have missed is that what’s the point of including first aid in the NPLQ if we then question whether they can give first aid? Of course they can. I suppose the emphasis on the HSE approach is the provision of first aid to ‘employees’, whereas the lifeguards are more likely to be providing the assistance to ‘customers’, and I would argue, generally for potentially more serious incidents. At our leisure centres we have a mix of both HSE qualified FAW and NPLQ lifeguards who work together and complement each other. It would of course make sense if the NPLQ course were to be validated to at least EFAW standard. Overall I would have more confidence in the NPLQ for the more serious incidents as they train every month in rescue and CPR etc. As a generalisation I suggest that many FAW, EFAW go from refresher to refresher with little experience of any significant incidents and no retraining in between. A lifeguard or anyone else for that matter can be appointed as an appointed person; they simply have to be, errr appointed! No significant training required. No first aid training required.