The p + tab is done using emmet mode and I got it working with eex, haml and react files. My .spacemacs file is pretty messy but I think I got it working with this customization or this one. Hope it helps.
And these lines are to enable it in react and haml.
(add-to-list 'auto-mode-alist '("\\.erb\\'" . web-mode))
(setq web-mode-content-types-alist
'(("jsx" . "\\.js[x]?\\'")))
;; Use emmet mode in other modes (React and Haml)
(add-hook 'react-mode-hook 'emmet-mode)
(add-hook 'haml-mode-hook 'emmet-mode)
