Perhaps:
(defun linearparam-p ( blk / ent )
(and (setq ent (tblobjname "block" blk))
(setq ent (cdr (assoc 360 (member '(102 . "{ACAD_XDICTIONARY") (entget (cdr (assoc 330 (entget ent))))))))
(vl-some '(lambda ( x ) (and (= 360 (car x)) (= "BLOCKLINEARPARAMETER" (cdr (assoc 0 (entget (cdr x))))))) (dictsearch ent "acad_enhancedblock"))
)
)
_$ (linearparam-p "dynamic_block")
T