Cary, welcome to the forum!

If the 'Sika- stuff' is waterproof, durable, not too expanding (which might crack the PVC), and good for your expected temps - I'd say 'go for it!'

What I've done in the past for hydrolic cement is to coat the interior of the hole (but not the last ~2 -3") with silicon, to waterproof it, and then used a 'pastry bag' to apply the hydrolic cement.

Please be sure to secure the pipe before applying the filler! I'll leave the pipe long in the back and fully secure it, then brace what's exposed in the pool. You want this to be flush to the pool surface, so make sure it is before applying the product and will remain so until the product fully cures. To keep the pipe debris free, use a threaded plug poolside (to protect the threads) and dry cap the other end.

I wish you well with your project! We'll be here to help/ advise. Any chance of posting a few pics of your process?