As shown in the following example, on a big catalog table,
MariaDB is able to use several indices at the same time
('...' are obfuscated unique values):

  > analyze select SQL_NO_CACHE uid, relative_url from catalog where reference='...' OR relative_url='...';
  +------+-------------+---------+-------------+------------------------+------------------------+---------+------+------+--------+----------+------------+--------------------------------------------------+
  | id   | select_type | table   | type        | possible_keys          | key                    | key_len | ref  | rows | r_rows | filtered | r_filtered | Extra                                            |
  +------+-------------+---------+-------------+------------------------+------------------------+---------+------+------+--------+----------+------------+--------------------------------------------------+
  |    1 | SIMPLE      | catalog | index_merge | Reference,relative_url | Reference,relative_url | 768,767 | NULL |    2 |   2.00 |   100.00 |     100.00 | Using union(Reference,relative_url); Using where |
  +------+-------------+---------+-------------+------------------------+------------------------+---------+------+------+--------+----------+------------+--------------------------------------------------+
  1 row in set (0.00 sec)

So mixing different dependency types with OR should be fine
(no need to split into more subqueries and join with UNION).